Download computer glossary

yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Data remanence wikipedia, lookup

IPKversion30/04/17 03:47
24 bit true colour. Header up to byte 54 of the picture file. Byte 55 is
the first pixel of the picture. Pixels ordered as Blue, Green, Red. Pixels start in the bottom LHS of
the picture.
Files should have the two characters MZ right at the start which other
programs accept as proof that a file whose name ends in .EXE is executable.
"Software to connect information, people, systems and devices",(via
the internet) Bill Gates.
Three key pillars to .NET
.NET framework - generation of applications for the internet age. The heart of this is CLR Common Language Runtime
XML - Web services
Smart clients - access for the internet.
-1-pixel GIF
Used by sites and advertisers to track precise browsing and
movements without your knowledge. Not detected by cookie filters. Can also be used in e-mails.
Look for IMG tags with the height and width parameters set to 1
-3D adaptor
3D graphics adaptors work alongside existing video cards.
Third Generation Partnership Project
Can support services up to 2Mbps over distances of about 10km
Offers 15Mbps at up to 27km
-404 Not Found
The computer found the web site server but the page could not be
A form of Ethernet and IEEE 802.3 network cabling using thin coax.
The term refers to 10Mbps (speed) Baseband (transmission) 200m max. length, (in practice 185m).
Up to 30 devices can be connected per segment length. The cable has a characteristic impedance of
50 ohms. Commonly called Thin Ethernet or Cheapernet.
A form of Ethernet and IEEE 802.3 network cabling using thick coax.
The term refers to 10Mbps (speed) Baseband (transmission) 500m max. length. Commonly called
Thick Ethernet. Ensure that all MAUs are at least 2.5m apart so that stations do not get lost due to
standing waves. If joints are essential try to distance them at special magic multiples of 23.4m as
this cuts standing wave effects. Also 50 ohm cable.
A form of Ethernet and IEEE 802.3 network cabling using twisted
pair cabling. The term refers to 10Mbps (speed) Baseband (transmission). 10BASE-T recommends
a segment length of 100m. Only two pairs actually used, connected to pins 1,2 and 3,6 avoiding
use of the common telephone pair 4,5. Twisted pairs have an impedance of 100 ohms.
10Gbps Ethernet.
A form of Ethernet and IEEE 802.3 network cabling using
twisted pair cabling. The term refers to 100Mbps (speed) Baseband (transmission). 100BASE-T
recommends a segment length of 100m. Expect transmission speeds of about 100MB in 1 minute
on a 100Mbps network.
Gigabit Ethernet. Utilises all four pairs and transmitting 250Mbits per
Protocol for fibre optic gigabit connections.
Power over LAN. Provides power for devices as well as Data.
Protocol for copper gigabit connections.
Advanced Audio Coding. Used for on-line music stores. Based on
Mpeg4 technology. Gives greater audio fidelity than MP3 but has digital rights management inbuild
to prevent multiple distribution.
Advanced Configuration and Power Interface. Enables PCs to start
quickly and have advanced power management facilities. Some reduce clock speed when full
processing power is not required.
Attenuation to Cross talk Ratio.
To close down an Acrobat Document in a web browser, right click the
Acrobat symbol on the task bar and select Close.
Anti-terrorism, Crime and Security Act, 2001
Alien Cross Talk is a feature of bundled cables.
-Active Directory
Replaces WINS and NT domains on win2000 and aims to give users
access to permitted resources using a single logon process. Allows businesses to manage security,
applications and privileges over the company network. The directory structure is created using the
DNS mechanism. It is non-reversible. Active directory is managed through Microsoft's
management console.
Steps to planning AD.
Create a forest plan
Determine the number of forests
Create a changevcontrol policy for each forest
Create a domain plan for each forest
Determine the number of domains
Choose a forest root domain
Assign a DNS name to each domain
Plan DNS server deployment
Optimise authentication with shortcut trusts
Create an organisational unit (OU) planh for each domain
Create OUs to delegate administration
Create OUs to hide objects
Create OUs for group policy
Create a site topology plan for each forest
Define sites and site links
Place servers into sites
Active directory is based on Lightweight Directory Access Protocol (LDAP).
Active directory is a directory service which stores information about network devices, resources
and users.
A set of interactive technologies developed by Microsoft, combining
OLE (Object Linking and Embedding) and COM (Component Object Model). Unlike Java,
ActiveX is not a programming language, but a set of instructions on how an object should be used.
ActiveX controls can be downloaded from the Internet, and run just like Java applets. However,
Java only interacts with the Web browser, while ActiveX controls can access the Windows
operating system.
A modern programming language designed for large, long-lived
applications - and embedded systems in particular - where reliability and efficiency are essential.
Based on Pascal and Algol, it was first developed by Honeywell-Bull to replace the many languages
used by the US Department of Defence. It was named after Augusta Ada Lovelace, regarded by
computer historians as the first programmer. The latest version is ADA2005.
The device that connects a piece of equipment to the network and
controls the electrical protocol for communication with that network. Also called a Network
Interface Card (NIC)
Additional Decryption Key
-Adobe Acrobat
Built on PostScript, a page description language.
Advanced Digital Recording. Philips format for back up tapes.
Active Directory Service Interfaces. A set of interfaces that enables
developers to query and manipulate directory service objects.
Asymmetric Digital Subscriber Line. You have to be within 5.5km of
an ADSL exchange to get a 512kbps service. If closer than 3.5km can get 2Mbps. It is the total line
length and not the distance to the exchange that matters. The line to the exchange must also be of
good signal quality. Dial 17070 and select options 3, 1 and 2, then BTs system will check the length
of the line and call you back with the results. See DSL.
Advanced Encryption Standard
Antiferromagnetically Coupled. When Ruthenium is layered three
atoms thick between the two magnetic layers of the disk platter it stabilises the storage medium
which would otherwise be prone to errors arising from small temperature changes. This occurs
when the density reaches 20-40Gbits per square inch. Significantly increases the storage capacity of
hard disks.
Advanced/Accelerated Graphics Port. Designed for 3D graphics
cards, the AGP slot will award special priority to the graphics card so that it doesn't have to compete
with everything else in the system, thus maximising the PCs video processing speed. AGP graphics
cards can access system memory directly as well as their own memory. AGP 2X has a peak transfer
rate of 512MBps while the AGP 4X runs at 1.1GBps.
Artificial Intelligence. See Brain
AppleMac Wireless Network System.
Advanced Intelligent Tape. Sony's back-up tape format. A helical
scan system. AIT-2 cassettes have a capacity of 50GB and a transfer rate of 6MB/s. AIT-3
expected to have capacity of 100GB per cassette and a transfer speed of 12MB/s. AIT's Memory is
Cassette (MIC) is a small flash ROM chip mounted in the cassette that allows access to indexing
and system log information without accessing the tape
Asynchronous Javascript plus XML. A collection of technologies and
techniques intended to make web applications as responsive, interactive and rich as their desktop
equivalents. Instead of reloading the page each time a user makes a small change, Ajax enables
small amounts of data to be exchanged with the server asynchronously.
Originally developed by Jesse James Garrett in his article in 2005 entitled Ajax: A New Approach
to Web Applications. The current most high profile user is Google.
The unwanted jagged appearance that may affect diagonals in images
displayed on the computer. Removal of the notchy effect is called anti-aliasing.
Occurs when there aren't enough pixels to represent a smooth line. There are several ways of antialiasing, from calculation intensive edge-anti-aliasing to the more common FSAA (Full Scene AntiAliasing) first implemented by 3dfx. Modern graphics cards generally fall into two categories Supersampling and Multisampling. Both are algorithmic approaches requiring some GPU
Supersampling anti-aliasing - used by Nvidia's GeForce2 series and Radeon 7000 series of graphics
cards. The picture is internally rendered at a higher resolution ie 4x, so that an 800 x 600 scene is
rendered internally at 1600 x 1200 pixels, with each pixel of the original scene subdivided into four
subpixel samples. Each of the four sub pixel samples contains separate colour data, so the final
pixel colour is determined by blending the samples. This blurs transition boundaries which appear
less jagged. Very demanding on hardware especially at high resolution.
SmoothVision is a version of SuperSampling, where randomised samples are taken rather than from
an ordered grid.
Multisampling supported by Microsoft in DirectX 8. It increases the resolution by storing copies of
the screen which are slightly shifted in the x and y axes. Multisampling concentrates on subpixel
edge coverage ie by averaging the intensity. This can lead to some loss of quality compared to
Supersampling, but the bandwidth requirements and hardware demands are less.
Adaptive Lossless Data Compression
Algorithmic language - developed in 1958. The first to use formal
grammar and block structure. Not used today. Pascal is probably the closest derivative and is the
language behind Delphi. C was also developed from Algol in 1972 but is more cryptic than Pascal.
See C++
-ALT *
Print Screen
Spacebar + c
Spacebar + m
Spacebar + n
Spacebar + s
Spacebar + x
Switches between a window and a full screen.
to view the properties of a selected item
Cycles through the apps in the order they were started.
Copies an image of the active window to the clipboard.
Displays the program's System menu
Closes the active window
Moves the active window with the arrow keys
Minimises the active window
Resizes the active window with the arrow keys
Maximise the active window
Switches between programs.
-ALT Gr key
In combination with a vowel gives that letter with an acute accent.
It also does the same job as pressing CTRL + ALT.
Active Messaging Library
Audio Modem Riser. Now usually replaced by CNR
American National Standards Institute
Wireless Access Point - supports up to 35 concurrent users over 100m
Web server for UNIX. Also a version for Windows.
Application Program Interface. A common interface that allows
programs to make use of services provided by the operating system or other applications. Winsock,
is an API that allows Windows and other programs to talk to TCP/IP for internet access.
They provide a library of ready made functions and tools that programmers can use. For graphics
processors examples are OpenGL and Microsoft's DirectX
-Aperture Grille
Use a horizontal grid of fine metal wires that run up and down the
screen to direct the beam. This grid creates slots that have the same effect as the holes found in a
shadow mask. To hold the grid in place, two fine wires run vertically across the top and bottom of
the screen which can sometimes be seen. Image sharper and brighter than shadow masks and tube
face is flatter.
Orange orangeinternet
Application Performance Management
Access Point Name of a GPRS network. For O2
Vodafone internet
Asia Pacific network Information Centre
Advanced Peer to Peer Communication. A network architecture
definition by IBM.
A program designed to be executed from within another program.
Cannot be activated from an operating system. Written in Java. Adhere to a set of conventions that
lets them run within a Java-compatible browser.
Used to configure Apple Mac computers into small workgroups.
Uses specialised cables and network interface cards to transmit data at speeds around 230Kbps.
-Application Layer
The highest layer of the seven layer OSI model structure with all user
or application programs.
-Application server
Runs an application for a client.
Audio Processing Unit
an FTP search engine invented in 1992.
Address Resolution Protocol. Consider two machines, A and B
sitting on the same IP network. When machine A starts to transmit IP traffic to machine B it
examines the destination IP address. As machine A knows that machine B is on the same network,
it has to find out B's Ethernet address. It sends out a broadcast ARP request to all machines on the
Ethernet network, essentially asking "who has B's IP address?". All machines on the network get
the request and check their IP address. When B finds that it is being contacted, it sends a response
back to machine A. A now builds an Ethernet frame and puts the IP packet in the payload field.
The frame is then sent over the Ethernet network to machine B. When B decodes the frame, the IP
packet is passed up to the IP software and dealt with in the usual way. There are several ways to
improve the efficiency of this process. All machines maintain an ARP cache. Everytime a machine
wants to send a packet it checks the cache to see if it has the correct mapping. If it does then it does
not send out an ARP request. Because IP addresses can be assigned to different machines, the ARP
cache has to time out at regular intervals. ARPs can also be setup so that each machine broadcasts
its IP/Ethernet address mapping on boot. This causes each receiving machine to add the mapping
into their local ARP caches.
ARP runs into trouble when routers are involved. Routers will not pass on Ethernet broadcasts
which makes it difficult for devices on different subnets to communicate. The workaround is to
have the router respond to all ARP requests for foreign networks. From this point on all machines
will quite happily send further packets to the router. This means that routers, and switches have to
be able to store thousands of address mappings locally. In a switch this is used to help the switch
pass the correct frames out of the correct port. See RARP Reverse Address Resolution
The forerunner of the Internet. ARPA is the Advanced Research
Project Agency, the US department of Defence Agency that funded the development of the first
computers to link networks across great distances.
Automatic Request for Retransmission
Advertising Standards Agency.
American Standard Code for Information Interchange. Most often
encountered as the ASCII character set, a group of 96 lower and uppercase characters plus 36 nonprintable control characters.
Application Specific Instruction Processors
Application Service Provider.
Active Server Pages. Supported by windows 2000 and Microsoft
Internet Information Server. Based on VB Script and initially released in 1996.
ASP instructions have to be placed with <% and %> tags. The code works by calling a standard
object such as a response or request followed by a method you wish to invoke separated by a dot, as
well as any further parameters in brackets. eg
<% Response.Write("Hello world!")%>
Pages are compiled, overcoming the poor performance limitation of
'classic' ASP.
An ASP application is essentially a set of pages containing controls. Most code is done on the
server rather than on the user's machine, and the HTML produced will work with any browser.
Translates from a low level language to machine code. It produces an
object code file.
-Asynchronous Transmission
Transmission in which time intervals between transmitted characters may be of unequal length.
Transmission is controlled by start and stop bits at the beginning and end of each character
AT Attachment. First introduced in 1986.
ATA-4 introduced in 1997 - also known as UDMA or ATA33. Data transferred at 33MB/s
ATA-5 introduced in 1998 - also known as ATA66 - runs at 66MB/s. This has an 80 wire cable.
The cable is colour coded. The blue plug goes to the motherboard, the black is the master and the
grey is the slave. Despite the rating, the maximum speed for any parallel HDD is around 45MB/s in
Advanced Technology Attachment Packet Interface. A standard for
connecting a CD-ROM drive to an Enhanced IDE adapter.
-Athlon processors
Use Socket A which contains 462 pins
Asynchronous Transfer Mode. A high speed networking technology
that transmits various kinds of information by creating packets of data. Can be extended to an
almost indefinite distance. Uses fibre optic cabling to deliver data at 155Mbps. A method for the
dynamic allocation of bandwidth using a fixed sized packet (called a cell). Uses 53-byte cells. This
was used over fibre by carriers in the 1990s, but was never popular with end users since it required
the displacement of existing Ethernet networks. Subsumed by standard IP packets.
Automated Teller Machine
Access through Share. Share permissions in WinNT. Independent of
any local NTFS or directory level permissions. More limited than NTFS directory shares.
Advanced Technology Extended.
The decrease in the strength of a signal over the length of a cabling
channel and is caused by a loss in electrical energy in the resistance of the cabling channel and by
leakage of energy from the channel
Attachment Unit Interface. Normally a 15way D type connector as
the interface between the Ethernet transceiver and the network device.
Acceptable User Policy
It is a series of instructions:- tells the PC which software
drivers to load, how much memory to use as buffers, etc
It is the second file to be loaded when the PC is turned on.
Prevents the same document being opened more than once at the same time. Uses about 10K
of base memory.
LH /L:1,32096 C:\SBCD\DRV\MSCDEX.EXE /D:MSCD001 /M:8 /V
Makes the CD-ROM drive work. The /M:xx switch tells DOS to use a section of memory as
a buffer for information coming from the CD-ROM drive. the higher the figure, the more the
buffer is, and that means the faster the CD seems. A good figure is 10 to 100.
SET BLASTER=A220 I5 D1 H5 P330 T6
Sets the rules for the sound card for when other software is looking for it.
Stops autoexec.bat file being echoed on the screen.
Tells the PC to display the full path in the prompt, ie C:\DOS>
Loads the mouse driver especially for DOS.
Sets the mouse type????
A listing of directories in which DOS looks whenever a command is typed. It first looks in
the WINDOW directory then the DOS directory.
Sets the TEMP directory for programs that need to store temporary files.
LH /L:0;1,45456 /S C:\WINDOWS\SMARTDRV.EXE /X 2048 128
Smart drive loads commonly used information into the machine memory, where it can be
accessed faster.
Refers to the way in which DOS characters are displayed on the screen.
Same operations as above.
Converts characters on the screen to English.
Create a text file named autorun.inf in the CDs root directory. The
first line of the file should contain only the text [autorun] To run a program type open= eg to run
explorer automatically the file should read
open=explorer.exe /n,/e,.
(yes comma and full stop!) The n means open in a new window and the e tells explorer to open in
expanded view.
A full list of commands for autorun can be found at
The Windows presentation subsystem in Windows Vista.
-Average Seek Time
The average time it takes the drives head to find the data on the drive's
-AV Ready
A drive that is able to transfer a minimum of 3MB/s, which is the
amount required for broadcast quality video.
Audio Video Interleave. Movie standard. Windows native format.
High quality video and sound but large files. Not supported by Macs. Designed by Microsoft to
combine audio and video in a single track or frame to keep them synchronised.
The part of the network that carries the heaviest traffic. Used to
connect different sections of LANs together.
Facility in Windows. Located in Start, Programs, Accessories, System Tools.
Son 1 Monday
Every Monday
Son 2 Tuesday
Every Tuesday
Son 3 Wednesday
Every Wednesday
Son 4 Thursday
Every Thursday
Father Week 1
Father Week 2
Father Week 3
Father Week 4
Father Week 5 (if needed)
Grandfather Month 1
First Friday
Second Friday
Third Friday
Fourth Friday
Fifth Friday
Last Business day Month 1
Grandfather Month 2
Grandfather Month 3
Last Business day Month 2
Last Business day Month 3
Set A
Set B
Set C
Every Other Day
Two Days
Every Fourth Day
Four Days
Every Eighth Day
Eight Days
Set D
Set E
Every Sixteenth Day
Alternate with Set A
Sixteen days
Thirty two Days
-Back plane
8 bit
16 bit
32 bit
32 bit
32/64 bit
64 bit
8 - 10 MHz
Connects balanced to unbalanced cables.
The maximum amount of data that a network cable can carry.
Microcode architecture used by Intel on its mobile processor chips.
First patented in 1949. RCA demonstrated the first barcode (a bulls
eye) in 1971. IBM developed the UPC (Universal Product Code) barcode system which became the
industry standard in 1973.
In Europe we use a variation of the EAN (European Article Number) of the UPC. The UPC/EAN
code used on retail products is an all numeric code. Code 39 includes upper case letters, digits and
a few symbols. Code 128 includes all ASCII characters.
A barcode always conforms to a fixed format. Eg around an EAN-13 barcode are four corner marks
that form a rectangle. These define the printable area for the code. Inside these are the so called
quiet zones, a clear border devoid of marks. On the left, middle and right of the code are special
bars called guard bars. The left and right guard bars indicate the beginning and end of the code,
while the centre guard bars separate the code into two zones. The actual number that the code
represents is printed at the bottom. This too has a fixed format - the first two characters are the flag
characters, which identify the country of origin. The next ten characters are called the data
characters, the first five of which identify the manufacturer and the last five identify the product.
The last character is the check-digit for the check sum.
The practical limit for a standard barcode is 20 to 25 characters.
A transmission technique employed in LANs. Only one device can
communicate at one time and a device simply sends its digital signal on to the cable without any
Computer language. Written by John George Kennedy and
Tom Kurtz in 1964. Qbasic is on the W95 CD in the folder \ other\Oldmsdos.
Uses an interpreter instead of a compiler to translateprogram statements to machine code and
execute them one line at a time.
Developed into Visual Basic in 1991 by Microsoft to simplify development of windows programs.
-Batch files
To make close automatically, right click the batch file in Explorer and
choose Properties. Click the program tab. Check the box for Close on exit.
For a program to run undisturbed until it finishes and closes add the command start/w to the
beginning of the line. To make a pause use the line choice/n/t:y,xx where xx is the pause in
Batch files expect windows programs to multitask so they won't wait for one to close before the
next starts. To make a program finish before the next one starts add the command start/w. To close
a batch file window when it has finished end it with the command CLS. This command must be the
only item on the last line - it should not have a return after it.
Can be created in any version of DOS above 5.0.
With W95 a windows program can run from within a batch file. Programs can run sequentially or
simultaneously. By default, batch files expect Windows programs to multitask. To make a program
finish before the next begins add the command start/w at the beginning.
A batch file is a script file containing anything that you might type at the DOS prompt, and each
command must be on its own line.
Create a batch file in Notepad or Edit. Save with the extension .bat. To edit a batch file, right click
the file's name in Explorer and select Edit. This summons the file in Notepad.
ping > ping.txt
find "TTL" ping.txt
goto ping%ERRORLEVEL%
If TTL found then ERRORLEVEL = 1. If TTL not found then ERRORLEVEL = 0
XCOPY the switch /D ensures that if the file already exists on the target disk then it is not
recopied unless its date is more recent. /S forces XCOPY to look in sub directories.
If using long file names, enclose the whole path in quotes " "
ECHO OFF stops subsequent commands being displayed on the screen. Typing @ECHO OFF
stops the ECHO command itself appearing.
Starting multiple programs from one batch file:eg start C:\windows\notepad.exe
start C:\windows\calc.exe
Unit of signalling speed. The speed in baud is the number of line
changes or events per second. Usually greater than the bit rate.
-Bell 212
An AT&T specification of full duplex asynchronous or synchronous
1200 bps data transmission for use on the public telephone network.
Backbone Edge Node - key connection points on the JANET
backbone. The BENs are managed by UKERNA as JCPs.
Bit Error Rate Testing/ Block Error Rate Testing. An error checking
technique that compares a received data pattern with a known transmitted data pattern to determine
transmission line quality
Ball Grid Array
Border Gate Protocol
Border Gateway Protocol 4 - a path vector protocol and works on the
principal of routing tables.
Browser Help Objects. .dlls that allow developers to customise and
control Internet Explorer. A list of malware BHOs is available at
Berkeley Internet Name Domain. The dominant DNS software used
on the Internet
Basic Input Output System. Software, usually held in ROM which
tells the operating system what hardware components the PC has. Also provides keyboard and
video control when PC is first switched on and provides checks on resources.
Back door passwords:
Award BIOS (upper and lower case) award sw, award_sw, award pw, _award, award?sw,
AMI BIOS (upper and lower case) ami, a.m.i., aaammmiii, ami sw, ami_sw, bios, password,
biostar, biosstar.
Phoenix BIOS phoenix, cmos, bios
Also try clearing the password. Boot to MS-DOS, type Debug then for an AMI or Award Bios enter
0 70 17 0 71 17 Q
For a Phoenix Bios enter he following code, using he capital letter O not zero O 7O FF O 71 17 Q
Built In Self Test.
Binary digIT. Invented by Claude Shannon.
Industry initiative to integrate business applications and processes -
adopted by Microsoft
Technology that eliminates the need to buy separate power supplies,
fans and management cards for every different server you decide to put in a rack. Instead you just
pop blades with different network technologies into one chassis which shares power, cooling,
cabling and infrastructure management. Often designed to occupy one rack unit in height 1U or
Designed to provide a common standard for wireless communication
between all computing devices from PCs and printers to PDAs. Uses frequency hopping technology
to provide a bandwidth of 1Mbps over a distance of 100 metres. Developed by a special interest
group led by Intel, Ericsson, IBM, Nokia and Toshiba. Designed to operate in a noisy radio
frequency environment. Operates in the unlicensed ISM band at 2.4GHz with a gross data rate of
1Mbit/s on a shaped, binary FM modulation. Designed for an aerial power of 0dBm, but
spectrumspreading has been added to allow optional power levels up to 100mW by frequency
hopping in 79 hops displaced by 1MHz, between 2.402 and 2.480GHz. This bandwidth is reduced
in some countries. The maximum frequency hopping rate is 1600hops/s and the nominal link range
is 10cm to 10m.
The baseband protocol is a combination of circuit and packet switching, where slots can be reserved
for synchronous packets and each packet is transmitted in a different hop frequency.
Bluetooth can support an asynchronous data channel, up to three simultaneous synchronous voice
channels or a channel which simultaneously supports asynchronous data and synchronous voice.
each channel supports a 64Kbit.s synchronous voice link while the asynchronous channel can
support an asynchronous link up to 721Kbits/s in either direction, while permitting 57.6Kbits/s in
the return direction or a 432.6Kbit/s symmetric link. The voice channels use continuous variable
slope delta modulation (CVSD) voice coding scheme and never retransmit voice packets. Chosen
because even at a bit error rate of 4%, the CVSD coded voice is quite audible.
Bluetooth. Named after the 10th century Viking, King Harald Bluetooth who lived in Denmark
between 910 and 940AD. Because of Bluetooth's communication skills, Denmark and Norway
became Christian countries and united during his rule. Bluetooth or Blatand in the old Viking
language, means dark complexion - he had very dark hair. The first concept of the technology that
became Bluetooth was created in Lund in Sweden in 1994.
Bluetooth 2 likely to increase bandwidth to 2Mb/s
Bandwidth on Demand - the technique of inverse multiplexing to link
the two B channels of a ISDN line to form one high speed circuit capable of running at 128Kbps.
Boot Disk
Windows 3.1 Format a:/s
Also useful to have AUTOEXEC.BAT, CONFIG.SYS, WIN.INI and SYS.INI.
Windows 95 Left click Start, Settings, Control Panel, Add-Remove programs, Startup Disk Tab.
Insert disk then left click CREATE button.
To check disk, turn off computer. Insert disk into A: drive and turn on system.
Hard print copies of AUTOEXEC.BAT, CONFIG.SYS, WIN.INI and SYS.INI.
In Windows 95 the crucial files are SYSTEM.DAT and USER.DAT.
To create a boot diskette, insert a diskette into the A: drive. At the DOS prompt type SYS A: and
press enter. Also copy over FDISK and FORMAT.
Use Bootable diskette to start system.
Run FDISK.EXE from boot diskette.
Choose Create DOS Partition or Logical DOS drive.
Select Create Primary DOS partition. etc.
Then format hard drive by typing FORMAT C:/S, which will transfer the necessary system files and
make it bootable.
Format a floppy as a system disk (format a:/s. Create a config.sys file containing:
device=c:\windows\emm386.exe noems novcpi
If running Win3.1 and Dos6, then substitute your DOS directory for c:\windows.
Create an autoexec.bat file containing
prompt $p$g
path c:\windows;c:\windows\command
loadhigh keyb uk
Again substitute DOS directory for c:\windows\command if using DOS 6.22
Copy CD-ROM and sound card drivers from existing config.sys and autoexec.bat files. Replace
device statements in config.sys with devicehigh and in autoexec.bat replace load with loadhigh.
Copy the Set Blaster line in autoexec.bat. Set is a DOS command, not a program, so it does not
need loadhigh.
Insert a floppy disk. Open My Computer, right-click the A icon and select Format. Click
the Copy System files check box, then click start. When complete click Close twice.
In Notepad, open file Windows\Dosstart.bat, then save it as a:autoexec.bat. Look for a line
in the file containing 'mscdex.exe', then delete everything up to it - the first word in the line should
be 'mscdex.exe'. Remove all subsequent lines as well.
Copy the file Windows\Command\Mscdex.exe on to the boot floppy in the A drive.
Back in Notepad, open config.sys on the C drive and look for a device=command that might
be your CD-Rom drive. Save it as a:config.sys. Remove any path so that the line reads
device = file
The device=line refers to a file by its path and name - c:\nec_ide.sys for example. Copy that
file to drive A. Then remove the path from the line in a:config.sys. For example, if the line reads
'device=c:\nec_ide.sys/d:neccd0', trim it to device=nec_ide.sys/d:neccd0.
-Boot sector Virus
Infects the section of a floppy or hard disk that contains operating
system and file information. Each time an infected PC starts the virus can spread.
The Army's digitisation program
Towards the end of the 19th century, a Spanish scientist, Ramón y
Cajal revealed for the first time the structure of the brain. He found a mass of cells (neurons) with
long extensions (axons) that connected to numerous other neurons – some close by and others far
away. By the middle of the 20th century, the model of a trunk telephone exchange, with neurons
acting as switches was well established. When the electrical activity of individual neurons was
examined, it was found that they did seem to be working like switches, with each cell producing a
suitable electrical output when stimulated by a suitable number and combination of input
connections. Many modelling attempts were made using Boolean algebra.
At around the time of the start of the second World War there were two crucial publications:
A Logical Calculus of Ideas Immanent in Nervous Activity by two neurologists Warren McCulloch
and Walter Pitts, and A Symbolic Analysis of Relay and Switching Circuits by the communications
engineer Claude Shannon. These two papers established the whole field of digital logic and meant
that systems (including the brain) could be analysed in terms of the basic logic functions of AND,
OR and NOT. Unfortunately, there was one serious flaw in the work of McCulloch and Pitts – they
had assumed that the neuron was just a simple binary switch. In fact neurons behave more like nonlinear analogue devices or multistate, rather than binary, digital ones. It was not until the late 1960s
that the problems were fully recognised. The subject of Cybernetics, or control systems developed
at this time as a result of the joint work by computer and neuro-scientists.
In 1952 a book called Design for a Brain, was published by a British psychologist, W. Ross Ashby.
In this he applied the principles of logic in order to try to understand how the brain can produce
adaptive behaviour – i.e. how it can learn to modify its actions in the light of experience, rather than
just operate in a strictly rigid way.
There were also attempts by computer scientists to build intelligent machines using basic electronic
neurons called perceptrons. It all ended in the late 1960s when AI expert Marvin Minsky published
a criticism of the futile attempts to build such machines and neurologists realised that neurons were
much more complex that they had thought.
Comparison of a brain with a computer. The brain is not a synchronous device and does not need
regular clock pulses to keep its operations in step unlike a modern computer. Trying to establish an
effective clock speed for the brain by doing a simple calculation would show that the brain runs at a
clock speed of less than 100Hz! To compensate for this a brain is organised for massively parallel
computation rather than having to push everything through a single CPU.
There are around 1011 in a human brain and each of these is estimated to have an average of 103
connections to other neurons, giving a potential 1014 connections or synapses. However, it is
unknown how many are needed to perform any particular task or how many are available for that
The brain consists of many specialised areas, for vision, motor control, smell etc so the number of
synapses that can be recruited for a particular task will be just a tiny proportion of the total.
However, this is considerably better than any form of parallel processing that exists in electronic
Memory comparisons are also difficult to make. In the brain, memories are believed to reside in the
strength of synaptic connections and so there are around 1014 memory locations. In his book, The
Age of Spiritual Machines, Ray Kurzweil estimates that it would need about 10 bits to define each
synaptic connection, giving an equivalent total memory capacity of 1015 bits. This is unlikely to be
accurate since it can not be assumed that every neuronal connection is available for memory. It is
also likely that each synapse may be part of many different memory patterns, so the efficiency of
those synapses that are used for memory storage may be high. However, as an estimate, 1GB of
memory contains around 1010 bits. So 100,000 PCs, with 1GB of RAM, would have the potential
same storage capacity as a brain, or in terms of 100GB hard disk drives, only 1000 would be needed
for the same potential storage.
The brain is constructed as a vast neural network in which thoughts and memories are spread out
across the network rather than relying on the conventional von Neumann computer architecture of a
single processor and addressable memory.
Techniques for studying the brain have improved from the stage of examining the brains of dead
stroke victims to using brain scanning techniques. Two scanning techniques are available:
PET – Positron Emission Tomography and fMRI – functional Magnetic Resonance Imaging. Both
rely on the fact that more oxygenated blood flows to active neurons than to those that are not
working. PET needs the patient to be injected with water containing positron-emitting Oxygen 15.
Where there is more blood flow there will be more positrons emitted. PET gives a resolution of
around 7mm and needs a sample time of around 30 seconds.
fMRI relies on the slight difference in the magnetic properties of oxygenated and de-oxygenated
blood and has a resolution of around 2mm and needs a sample time of 10 seconds. The patient
needs to be absolutely still with each scanning method.
Basic Rate Interface - ISDN line configuration giving two 64Kbps
data channels and one 16Kbps overhead channel. Combines voice and data over a single service
Used to connect two or more LANs to form a larger LAN. Can
improve performance and security. Bridges function at the data link layer of the OSI model.
Multi-channel analogue transmission technique employed in LANs.
The signals on the network are divided, usually by frequency division multiplexing, to allow more
than one signal on the cable at any one time. Requires MODEMs for all devices wishing to access
the network.
=>2Mb/s down
=>8Mb/s down
=>24Mb/s down
=>1.8Mb/s down
=>4Mb/s down
=>4Mb/s down
=>2Mb/s down
=>2Mb/s down
=>384kb/s down
A client software program used to search networks and retrieve and
display copies of files in an easy to read format. They can also call upon associated programs to
play audio and video files. Microsoft Internet Explorer and Netscape Navigator are the most
commonly used.
British standard for data security
Bisynchronous Transmission. A byte or character orientated IBM
communications protocol. It uses a defined set of control characters for synchronised transmission
of binary coded data between stations.
Balanced Technology Extended.
An amount of memory that is used to store frequently used data.
-Buffer Overflow
A situation in which the buffer (a software stack used for holding data
while it waits to be transferred) becomes flooded with code that then leaks into a system's main
memory. This can result in code being executed.
Virus. Can disarm antivirus and firewall software. Has key logging
facility. Appears as an e-mail. Mails itself to recipients in e-mail address books.
-Bump mapping
This lets software make indentations in the scenery to add realism.
Waves can easily be added to water etc
The internal pathway for signals moving around inside a computer,
transferring data between various components.
In LAN technology, a linear network topology; contrast with ring or
star. All of the computers are connected to a single wire (or bus) which forms the central highway
for all network traffic.
-Bus master
An intelligent device such as a PCI adapter card that can gain control
of the bus and use it to transfer data without involving the processor.
Eight bits or binary digits. 1KB = 1024 bytes. 1MB = 1048576 bytes.
Microsoft Programming Language
First published in 1983. A derivative of Algol. Overcame some of
the short comings of C. Supported Object Oriented programming, a technique that allows complex
code to be encapsulated in simple to use building blocks called Objects.
A chunk of high speed memory used for speeding up operations in a
PC. External (L2) cache is on the motherboard and is often 512KB. AMDs latest chips have 2MB.
The fastest cache memory is Level 1 and is used for the most frequently used information. Usually
stored directly on a special section of the processor chip. Pentium IIIs have 32KB of L1 cache on
the processor chip and either 256KB of L2 on-chip or 512 of L2 off chip. For high end processors it
can take from one to three clock cycles to fetch data from L1, while the CPU waits and does
nothing. It takes six to 12 cycles to get data from a L2 on the processor chip and dozens or
hundreds of cycles for off chip L2. Intel planning in 2001 to introduce level 3 cache in its 64-bit
server processor called Itanium. The 2MB or 4MB cache will connect to the processor via a bus
that runs as fast as the processor i.e. 800MHz.
Allows users to hide and view sensitive data inside picture files to
prevent detection
Content Addressable Memory
Control Area Network
Computer Application program Interface
Enables PC cards (PCMCIA) to be hot swapped on notebooks.
Column Address Strobe. A signal which tells the DRAM to accept a
given address as a column address
-Category 3
Voice and data transmission up to 16MHz or 10Mbps.
-Category 4
Voice and data transmission up to 20MHz or 16Mbps.
-Category 5
Cabling to 100MHz. Must meet standards of the design definitions of
ISO 11801 and TIA 568-A. Must also meet the test definitions of TIA TSB67.
-Category 5E
Cabling to 100MHz, but must be able to pass greater tests. Provides
an improved Attenuation to Crosstalk Ratio (ACR) and return losses compared to conventional
-Category 6
Cabling to 200MHz.
-Category 7
Cabling to 600MHz.
Constant Angular Velocity. Used with CD ROM drives. Data on the
outside of the risk read faster than that on the inside.
Content Addressable memory. Designed to accelerate any application
that requires fast searches of list based data. Different to normal memory where data is stored in
specific locations called addresses. When there is a need to retrieve the data, an address is supplied
to the memory, which in turn returns the data. In CAM the opposite occurs. Data is supplied to the
memory via a special comparand register and the memory returns an address if a match is found,
enabling extremely quick searches to be made. The entire CAM is searched in a single clock cycle
Charge Coupled Device. Used in digital cameras to capture images.
Each pixel of the sensor stores an electric charge proportional to the amount of light that strikes it.
The brighter the light the higher the charge. At the end of the exposure, the charge is digitised and
assigned a brightness value. The pixels in most sensors only record brightness and are unable to see
colour. To make a colour picture, each pixel is normally covered by either a red, green or blue
filter. Groups of four pixels are arranged in a two-by-two 'Bayer' pattern featuring one red, one blue
and two green filters, since the green wavelengths contain the most image detail. The camera
software then interpolates the filter data to create a full coloured image.
Centre for Communication Interface Research
CD-Digital Audio
Single speed data transfer 150Kbps.
Spiral of tiny pits pressed into a plastic substrate starting from the middle and working outwards.
A typical audio CD about 5 billion possible pits. The plastic substrate is coated with a very thin
layer of aluminium. On a CD the pits are a minimum of 0.83microns long. DVD pits are
0.4microns and 0.74 microns apart rather than 1.6microns on current CDs.
DVDs currently hold 4.7Gb.
The substrate of a gold disk is similar to that of a silver disk. This substrate is covered first with a
thin layer of cyanine dye and a thin layer of gold is sputtered onto this layer of dye. When writing to
the disk a higher power red laser is used. When the equivalent of a pit is required, the write laser is
switched on and the energy in the fine beam is absorbed by a dot of cyanine dye which explodes and
creates a minute distortion of the gold layer.
Gold disks have a better signal to noise ratio than silver disks.
The ReWritable disk. They have a layer which can be either crystalline (which reflect light) or
amorphous which scatters the light. When erasing a disk a higher power laser converts the
amorphous areas back into the crystalline form. Not a very high signal to noise ratio and often only
readable on other CD-RW machines.
Original audio format devised by Philips and Sony - referred to as CD Digital Audio - CD-DA to
the Red book standard.
First computer CD-ROMs also defined by Philips and Sony to the Yellow book standard.
Yellow book defines three standards:
Mode 0 rarely used. Almost the same as CD-DA.
Mode 1. CD-ROM (Mode 1) The data is held in blocks of 2352 bytes of which 2048 bytes, starting
at the 17th byte, contain the important data. The 276 bytes at the end of the block contain codes
which can be used for error correction in the main block. This gives an estimated error of 1 bit in
200 CDs!
Mode 2. Rarely used, error correction coding sacrificed.
Yellow book extended to give CD-ROM XA format.
Most popular form CD-ROM XA (Mode 2) (Form1), even though it is different to the formal mode
2 format. The main difference in the software required to read CD-ROM (Mode 1) and CD-ROM
XA (Mode 2) (Form1) is that the 2048 data bytes start on the 25th byte instead of the 17th byte.
A system which will read CD-ROM XA (Mode 2) (Form1) will also read Philips CD-I and Kodak
CD Extra format: written to the Blue book standard. Multi-media. Also called CD Plus and
Enhanced CD.
The audio tracks are laid down first in CD-DA format and the data track in CD-ROM XA (Mode 2)
(Form1) format is laid down afterwards. Such disks can be played on standard CD players. A
computer will read the last track first
Multi session. Works by writing a table of contents (TOC) to the disk at the end of the first session.
In subsequent sessions files not in TOC or modified are written to the disk and a new TOC written.
Since the software should read the last file first, the latest TOC will be read.
Each session on a CD-R disk takes a lead in track of about 13Mb
To make a CD autorun. Create a file in the CD root directory named autorun.inf In the file put
The 'open=' shows the path and filename of the application to be launched when a disc is inserted
and the 'icon=' lets you specify your own icon for the CD-ROM drive in Windows Explorer
Channel Definition Format - developed by Microsoft. Describes the
content and properties of Push channels using XML mark-up.
Code Division Multiple Access
Collaboration Data Objects
ISO standard.
ISO level 1 allows forfilenames of up to eight plus three characters.
ISO level 2 allows for file names of up to 31 characters
Code Excited Linear Predictor. Used for speech coding in VoIP
Central Office Exchange service is a type of PBX service where
switching occurs at a carrier's local telephone exchange instead of at the company premises.
To get the Centrino badge a notebook must contain three components:
the Intel Pentium-M processor, the Intel 855 family chipset and the Intel PRO/Wireless 2100
Network Connection. A 1.6GHz Centrino noetbook will always outperform a 2.4GHz Pentium 4-M
notebook. The Pentium-M processor is like a combination of a Pentium-III-M and the Pentium 4M. The processor gets more performance per clock cycle (courtesy of the Pentium-III) and a quad pumped 400MHz front side bus and support for SIMD and SIMD2 instructions from the Pentium
4). The system also provides extended battery life.
Chinese Education and Research Network.
-CGI scripts
Common Gateway Interface. Small programs that run on a web
-Characteristic Impedance
The impedance that a channel would have if the channel were infinitely long.
See 10BASE2. Uses a thinner, lower cost cable.
Classless InterDomain Routing. Used for subnetting
an exact colour scale.
Common Internet File System. Also referred to as SMB
Common Interface Model
Cross Interleaved Reed-Solomon Code
Card Information Structure. Information about a PCMCIA card that
is passed to the host computer when the card is inserted
Contact Image Sensor - employs dense banks of red, green and blue
LEDs to produce white light and replace the mirrors and lenses of a CCD scanner with a single row
of sensors placed extremely close to the source image.
Complex Instruction Set Computer
Supplier of client computing
Certified Internet Webmaster
Compulink Information Exchange
Corporate License Agreement
CyberLink Eagle Vision. Used on Power DVD. Intelligently adjusts
contrast and colour in a movie and balances darker and lighter areas. Makes hefty demands on
Common Language Interface. Microsoft.
CyberLink Pano Vision. Used on Power DVD. Compensates for the
problem of watching 4:3 aspect ratio films on a widescreen display by stretching the video at the
screen edge, leaving the central part of the movie untouched. Also used on WinDVD
Common Language Runtime - the heart of the .NET framework.
A Node on the network, such as a user workstation, that uses
resources provided by the server
Caller Line Identification Presentation
(allocation units) Data is stored in clusters ranging from 2KB to
32KB, depending on disk size.
Constant Linear Velocity. Used with CD ROM drives. Ensures that
the data is read at a constant speed. Used on early CD ROM machines.
Computer Misuse Act.
Core Management Environment. Phoenix's replacement for BIOS.
cyan, magenta, yellow and keystone black.
Communication and Network Riser
Cache On A STick. Used to upgrade level 2 cache.
The first programming language for business use. Developed in 1960.
A development environment for building and deploying web
applications and web services. Now part of the Adobe/Macromedia family and integrated with
products such as Flash, Dreamweaver and Acrobat. First released by Allaire in 1995.
Coldfusion has its own tag-based server-scripting language, Coldfusion Markup Language (CFML),
with a syntax that closely resembles HTML and XML
-Collaborative network Allows other users to share resources, i.e. processing power. Used in
Exchange Server and SQL server
The result of two stations attempting to use a shared transmission
medium simultaneously.
Computer developed during WW2 by Tommy Flowers and used to
crack German coded messages. Designed, built and installed in 9 months it contained 1500 valves.
Ten were built and 8 were dismantled straight after the war. Two went to GCHQ and were
subsequently dismantled in 1960. Tommy Flowers (1905 - 1998) was an engineer for the General
Post Office (GPO) and after the war returned to the Post Office and worked on telephone
Component Object Model - a means of communication between
software objects. Microsoft. Provides inter application communications between software running
on the same machine. e.g. a Word document can embed a live spreadsheet from Excel, or Internet
Explorer can display a Powerpoint slide.
Interprets DOS commands.
-Compact Flash
Memory card. First released in 1994 - 3.3V and 5V supplies. 3.3mm
thick. Type II cards are 5mm thick. These are primarily IBM microdrives.
Translates from a high level language to machine code. It produces
an object code file.
-Computer Misuse Act 1990
"Unauthorised access" refers to some-one bypassing a user name and password screen.
Section 1: "A person is guilty of an offence if
a). he causes a computer to perform any function with intent to secure access to any program or
data held in any computer;
b). the access he intends to secure is unauthorised; and
c). he knows at the time when he causes the computer to perform the function that that is the case.
Stored in the root directory.
A listing which tells the machine what hardware is installed, how to use the physical memory,
which version of DOS, etc.
It is the first file to be processed when the PC is turned on.
Lets DOS know it can load some programsinto High Memory
lets DOS use all memory over 1Mb.
If XX=RAM then memory can be used as both expanded and extended.
If XX=NOEMS then PC told not to use expanded memory (may be needed by some
Buffers are small (1K) chunks of memory which DOS can use to store information quickly
Not really needed any more.
The number of DOS files that can be open at any one time.
Tells DOS to use high memory whenever possible.
Tells DOS to use Upper Memory Blocks.
Should be used to tell the PC the name of the last drive on the system.
Specifies the number of File Control Blocks that DOS can use at any one time. Rarely used
or needed now.
Tells the machine about the CD-ROM drive.
Tells the system which country it is in.
Tells system to convert American characters to English.
-Contention ratio
The number of other users competing for bandwidth on a broadband
connection. A contention ration of 50:1 means that the available bandwidth is shared with 49 other
A cookie is a message sent by a Web server to a browser, and is
stored in a text file, usually called cookie.txt. The message is then sent back to the browser every
time a new request is made while still on the site. When you move to another site, the cookie stays
on the hard drive. When you return to the original web site the browser sends the cookie
information back to the web server. Cookies are mostly used to identify users and create site visit
statistics on types of browser, operating systems and popular pages.
Common Object Request Broker Architecture
Class of Service
Compact Peripheral Component Interconnect. Concept behind Blade
Customer Premise Equipment.
-CPU speed
Accessories - System tools - System info - Tools - Windows Report
A supercomputer. The T3E900 has 840 DEC Alpha processors
running at 450MHz. Twenty CPUs have 512MB of memory each and the other 820 have 128MB,
which makes a total of 115,200MB. It can perform 80,000 million calculations per second
Colour Resolution Enhancement Technology. HPs half tone printing
technology. Four levels of ink per pixel are possible.
Customer Relationship Management
-Cross linked files
When two or more entries in the FAT refers to the same allocation
units (clusters).
The unwanted transfer of a signal from one circuit, called the
disturbing circuit, to another, called the disturbed circuit.
The science of transforming data into an unreadable format by anyone
who does not have the correct key. Converts plain text into cyphertext. There are two basic types
of encryption, symmetric and asymmetric. Symmetric encryption uses the same key to encrypt and
decrypt the cyphertext.
Caesar cipher - substitution cipher. Letters are substituted for other letters in the alphabet. Can be
done by shifting the letters by x places in the alphabet or by defining a completely new character
map. Both methods redundant as they can be broken by checking the combinations. Basic Englishlanguage rules help 'e' is the most common letter, and the most common two-letter combinations are
'th', 'in', 'er', and 'an'. Knowing the subject of the cipher text also helps since specific words can
then be sought.
Transposition cipher - does not disguise the letters but rearranges them instead. First a word
without repeated letters is used as a key. The number of letters in the word is used as the number of
columns, with the columns numbered by the alphabetical position of each letter - 'a' equals 1 etc.
The plain text is written in rows and the ciphertext produced by reading the columns in numerical
order. To convert back the same operation is used in reverse, i.e. columns are populated in order.
For this to work the number of columns has to be known so the correct number of characters can be
put in each column. For the system to work the table has to be fully populated by putting random
characters at the end of the plain text to fill out the table. To uncover the code you have to break the
number the number of columns used as the key and then rearrange them until they make sense.
plain text
One-time pad - All encryption methods so far can be broken as they rely on simple character
replacement that retains patterns. Perfect encryption that cannot be broken - called the one-time
pad. This uses a randomly generated key that is the same bit-length as the plain text. An exclusiveor is then performed between each bit of the key and the plain text. Getting the plain text back uses
the same procedure which is perfectly secure for two reasons. First, standard cryptographic attacks
do not work because each letter is equally as likely to appear. Secondly, trying every single key
combination in a brute-force attack does not work, as each decryption is as likely to be correct. This
only holds out if the key is not divulged, and is only used once - hence the name. Theoretically,
encrypting multiple pieces of data could lead to statistical attacks breaking the key. The problem
with this is the key is unwieldy to carry around and cannot be memorised.
Symmetric algorithms - uses smaller - 64-bit upwards-keys to encrypt the data. The XOR
operation is fast and masks the contents of the packets so standard cryptographic attacks that rely on
identifying patterns of data do not work. The key must remain a secret, as anyone who knows it can
decrypt all of the data. These systems are called private-key encryption. RC4 and Data Encryption
Standard (DES) are the most popular. The speed of the encryption makes them suitable for use in
real-time applications such as VPNs.
Asymmetric encryption - symmetric encryption suffers from the problem that it is difficult to
distribute keys and any encrypted message can be read by all users with the key. Sometimes a
message needs to be encrypted so only the intended recipient can see it. Asymmetric encryption
developed in 1976 at Stanford University by Diffie and Hellman. The principle, also known as
public-key cryptography, works on the assumption that instead of having a single key to encrypt and
decrypt, there are two keys, one to encrypt and one to decrypt. The encryption key is known as the
Public key and any user wanting to send a message can use it. The decryption key is the private key
and the owner never divulges it. Any message encrypted with the public key can only be decrypted
with the private key and is secure in transit as only the intended recipient can read it. There are no
problems with key distribution as the public key is available and the private key is known only by
the owner.
The system has three requirements. Assume that 'm' is the message, 'E' is the public-key encryption
algorithm and 'D' is the private-key decryption algorithm. The three requirements are:
D(E9m)) = m anything that is encrypted with the public key can only be decrypted with the
private key. So E(m)/E does NOT equal m
It is extremely difficult to deduce D from E
E cannot be broken by a chosen plain text attack.
The most common public-key algorithm is named after its discoverers, Rivest, Shamir and Adleman
(RSA). The algorithm works by finding two large (e.g. 1024-bit) prime numbers. The large prime
numbers are used to create the two keys e.g.
Take two large prime numbers, 'p' and 'q'.
Calculate (p-1)(q-1).
Choose 'd' so that it does not share any prime factors with (p-1)(q-1). 'd' does not have to be a
prime itself, but it does have to be odd.
Compute 'e' where de =1 (mod (p-1)(q-1)). Mod represents the remainder part of a division e.g. 3
mod 2 = 1. But it can also be used to describe a number in modulas form as denoted by brackets. eg
25 mod 12 = 1 and 25 = 1 (mod 12).
The encryption algorithm is encrypt(m) = (me) mod pq, where 'm' is the plain text message and a
positive integer.
The decryption algorithm is decrypt(c) = (cd) mod pq.
Therefore for encryption you need (pq, e), the public key. Decryption needs (pq,d), or the private
key. eg (with small numbers!)
Let p = 3 and q = 11
(p - 1)(q - 1) = (3 - 1)(11 - 1) = 2 x 10 = 20
d has to be relatively prime to (p - 1)(q - 1) so 'd' has to be relatively prime to 20. Choose 'd' to be 7
as it does not share any prime factors to 20.
de = 1 (mod ((p - 1)(q - 1))
7e = 1 (mod 20)
7e mod 20 = 1
p x q = 3 x 11 = 33
This can be used to encode the plain text NETWORK.
Char Numeric
m3 mod 33
c7 mod 33
Due to the way the system works it can also be used for authentication. Digital signatures. First the
sender creates the message and computes its checksum, which is encrypted using their private key.
The message is encrypted using the recipient's public key and transmitted. When it arrives, the
recipient decrypts the message using their private key, then decrypts the checksum using the
sender's public key. If this works it proves the sender generated the message. Finally the checksum
is recalculated to ensure the message has not been tampered with.
Carrier Sense Multiple Access. A technique by which many work
stations can transmit over one cable without a controlling transmission authority
CSMA with Collision Detection. CSMA that also listens while
transmitting to detect collisions. Used in IEEE 802.3 Ethernet
Cascading Style Sheet. Language developed to bring more control
over screen presentation to HTML authors
Content Scrambling System. Used on DVD audio
Computer telephony Interface/Integration
drag a file
Esc + r
Select all
to a folder to copy a file
Goto end of document
Displays the Start menu
to open the Run dialog box
Close current document
Goto next open document
Goto beginning of document
Goto option in Windows Explorer
Goto beginning of next word
Goto beginning of previous word
Goto beginning of next paragraph
Goto beginning of previous paragraph
Inserts copyright symbol © (W97)
Inserts registered trademark ® (W97)
Inserts trade mark symbol ™ (W97)
Close program options
drag a file
Select to end of document
Goto previous open document
Select to beginning of document
Select word to the right
Select word to the left
Creates a shortcut to the file
Computerised Telephone Systems
Continuous Variable Slope Delta modulation (CVSD) voice coding
scheme. Even at a bit error rate of 4%, the CVSD coded voice is quite audible.
Coarse Wavelength Division Multiplexing. Has a channem spacing
of 20nm. Can be used for distances up to 75km. To have speeds of 10Gb/s, the data is split into 4 x
3.125Gb/s feeds. The multiplexers are based on either a prism or a tilted Micro Lens Array (MLA).
Invented by science fiction writer William Gibson, who defined it as
'a graphical representation of data abstracted from the banks of every computer in the human
system. It is the virtual universe of information transmitted by computers, programs, audio and
video media, telephone, television, wire and satellite.
Direct Access File system, a file sharing protocol designed to
improve the performance of network-attached storage systems.
Directed Attached Storage - a disk array directly connected via IDE or
SCSI to a server for content storage
Dynamic Adaptive Speculative Preprocessor
Digital Audio Tape. Two heads for reading and two for writing data.
Information is recorded onmini cassettes using a helical scan which spools a 4mm tape at speeds of
0.32in/s. The angle of the tape head results in a high density of data, around 4Gb, more if DDS
formating or DDS-2 data compression is used.
-Data Protection Act 1998
Individuals have the right to view sensitive information about themselves e.g. sickness records,
disciplinary and training records, appraisal notes, e-mail logs and general personal files.
A unit used by BT at the exchange that allows a single wire to be used
as a double line. Some reduction in quality but only half of the Internet speed.
Database software from IBM that runs primarily on Unix and Solaris
Data base Administrator - software which administers databases. It
carries out the maintenance of a database, including the applications and content structure.
Database Management System. The program which builds the data
base e.g. Access.
Data Circuit-terminating Equipment e.g. a MODEM - fitted with a
female connector. Data Communications Equipment.
Distributed Component Object Model. Within the Windows
operating system - enables one application to communicate with another by exchanging data and
providing services that can be invoked by other DCom-aware applications. DCom is the version of
the Com protocol that extends inter application communication to external computers so that a
client PC can call up a DCom-aware service running on a server
Dynamic Data Exchange. Allows programs using OLE to exchange
data dynamically.
Direct Dial Inwards.
Distributed Denial of Service attack. Tribe FloodNet and Trin00,
typical open source tools.
Double Data Rate RAM. Type of SDRAM in which data is sent on
both the rising and falling edges of clock signals. Used on video cards. Supported by 760 chipset
DDR technology and bus topologies have a maximum clock frequency of 200MHz, or 400Mb/s/pin.
This is commonly referred to as DDR400
Starts where DDR ends. DDR2 supports clock frequencies of
266MHz (DDR2-533) and future speeds of 333MHz (DDR2-667). By running dual channels a
potential throughput of 8.6Gbytes/s
To achieve the increase in clock speed, changes have been made to the architecture. The operating
voltage has been lowered to 1.8V + 0.1V. All DDR2 components use an FBGA package instead of
TSOP. On die termination is used to improve signal quality on the databus.
Has 240 pins instead of the 184 pins of DDR.
Algorithm for cracking CSS encryption. Also Speed Ripper
Digital Enhanced Cordless Telecommunications phone. also Digital
European Cordless Telephony. Operates within the 1.9GHz band and released for use in 1992
Directory Enabled Networking. Allows network managers to manage
bandwidth and prioritise traffic.
Data Encryption Standard. Devised by IBM in and adopted by the US
government in 1977. The best known example of secret key encryption.
-Desktop icons
To change Open Paint. New Select Pels as units and make picture 32
for both with and height. When complete save with double quotation marks as "newicon.ico".
Windows sees the ICO extension and automatically creates a 16 bit colour icon, shrinking the image
to fit as needed. To replace an icon, select through properties of the icon to change.
-Device driver
A piece of software that will let the operating system and programs
running with it, control a particular hardware device such as a monitor or a printer.
Dynamic Frequency Selection/Dynamic Channel Selection - allows
client devices to detect the clearest channels within the radio waveband. See IEEE 802.11h.
Dynamic Host Configuration protocol. A DHCP enabled server
automatically assigns internet protocol addresses to networked computers, so each networked PC
doesn't need an individual IP address to access the Internet.
Direct Sequence Spread Spectrum
Digital Home Working Group.
Dynamic Hypertext Markup Language
Differentiated Services. Used in VoIP. Overcomes the limitations of
ToS. It is a layer-3 protocol used at the edge of an enterprise which tags each frame, either at the
originating device or at an intermediate point, to identify the requested level of service. It includes a
Differentiated Services Code Point (DSCP) which specifies how each switch handles the frame.
-Digital Audio
DVD Video
DVD Audio
Different formats.
Resolution bit/sampling rate
five channel 24/96kHz
two channel 24/192kHz
Audio bandwidth
-Digital Radio
Broadcast at 256Kbps
-Digital Telephony
Usually an analogue signal is sampled every 125microseconds by an
8-bit ADC. Each telephone requires a 64Kbps channel.
T-Carrier First digital network. Introduced in the 1960s in America. Based on a 1.544Mbps T-1
line. System still in use. The line is divided into 24 x 64Kbps channels for voice communication
using Time Division Multiplexing. The channels are combined into one 192-bit frames plus an
additional bit to separate frames. 8000 of these are transmitted per second. Control signals are sent
by robbing 2-bits from the encoded voice signal.
E-Carrier Used in Europe. Uses 2.048 Mbps E1 line giving 32 x 64Kbps voice channels. Does
not use bit-robbing and uses the entire bandwidth for encoding the signal.
Digital Signal X describes digital transmission rates based on DS0, which is 64Kbps.
DSX Comparison
Digital Signal
Data Rate
DS0 multiple
-Digital Signal X
See Digital Telephony
-Digital TV
Each frame is split up into around 300,000 pixels. Each pixel is
assigned a code number made up of data bits that identify its position within the picture, its colour
and its light intensity. Therefore about 600kB are needed per frame and about 18MB per second.
Compression operates on the principle that there are multiple pixels within consequtive frames
which are identical. So these do not have to be transmitted every frame.
-Digital Video Formats Three main standards used by digital camcorders. DV25, MicroMV
and DVD-VR. DV25 is the most common and is used by all consummer MiniDV camcorders. It
uses a 5:1 compression that records video at a constant rate of 25Mbps. Requires around 13GB for
an hour recording. It is tape based - but good for editing since all of the frames can be read
Tape based MicroMV uses MPEG-2 compression and records at 12Mbps. The data needed for a
single frame of video may be spread across a series of frames so cross fades can require cross
calculation and rendering.
DVD-VR is another MPEG standard - data rate of typically 6Mbps.
Dual In line Memory Module. A memory board that is effectively a
double SIMM. It uses a 168 pin connector and its 64 bit wide bus allows single modules to be
installed in Pentium systems. A memory module with signal and power pins on both the front and
back of the board.
Video and sound card drivers.
Digital Image Stabilisation. Used on camcorders to reduce camera
shake. It works by looking at the detail around the edge of the frame to work out whether the image
is shifting. Also OIS
-Display adapters
MDA Monochrome display adapter. Each character was displayed in a 9 x 14 grid, with 80
characters per line and 25 lines per screen
CGA Colour graphics adapter. Each character was built on a 8 x 8 grid with maximum resolution
of 640 x 200 (standard was 320 x 200). Four colours.
EGA Monochrome text in 9 x 14 grid at resolutions of 720 x 350, but also CGA colours at 320 x
VGA 640 x 480 and 16 colours
SVGA 600 x 800 at 256 colours
-Distributed Computing Tasks completed locally on machines , not on server.
This is the process which uses dots in patterns to create different
An implementation of MPEG4. It can compress video to a
much greater extent than even MPEG2, while achieving much the same visual quality. Can support
frame sizes up to 4096 x 4096 pixels and is able to deliver high-definition footage.
Dynamic Link Library. A way of writing programs so that bits of
them- the functions in the library- can be shared between several tasks at the same time rather than
each task containing copies of the routines it uses.
To register a .dll file c:\windows\system\regsvr32.exe file.dll.
Most functions of the Windows API are made accessible by DLLs. Can be viewed by Quickview.
Used in Data projectors. Largely the creation of Texas Instruments.
The image is formed on the DMD (digital micromirror device) IC. The surface of this chip is made
up of thousands of tiny rotating mirrors and each of these represents an individual pixel which can
be rotated between an on and off position (10 - 12 degrees of rotation of the mirror are possible).
Light is directed onto the surface of the DMD IC and, as it hits the mirrors, it is either reflected onto
the screen or onto a light absorber. The image can appear fuzzy compared to LCD projectors but he
contrast ratio is greater.
Digital Linear Tape. Back-up tape format. The capacity of DLT
tapes is currently 35GB per cartridge with a transfer speed of 5MB/s for the DLT7000 and 40GB
per cartridge for the DLT8000. Super DLTs will be in service mid 2000 and will offer 100GB per
cartridge with a transfer rate of 10 to 20MB/s. Super DLT uses Laser Guided Magnetic Recording
(LGMR), which employs optical and magnetic methods to greatly increase the data storage capacity
of cartridges.
SDLT 220 drives can fit up to 110GB (uncompressed) onto each tape with transfer speeds of
SDLT 320 drives can fit up to 160GB (uncompressed) onto each tape with transfer speeds of
Digital Lempel Ziv - a compression system used on back up tapes.
Direct Memory Access. A process for data retrieval from a device
such as a hard drive that writes it into main memory without involving the processor, so freeing it
up for other tasks.
Direct Methanol Fuel Cells
Desktop Management Interface.
Differential Mode Termination is a way of terminating a modular
connector or cable in its characteristic impedance.
Desktop management task Force
Distributed iNternet Architecture Developed by Microsoft in 1998.
Domain Naming System. This is the system that turns the numeric
data that the Internet uses for web site locations into text the user can use, e.g. = The DNS is implemented as a hierarchical system of communicating nameservers.
Currently based on IP version 4 (IPv4) which gives the dotted quad numbers and has values in the
range 0 to 232 (four and a bit billion). DNS entries in DNS server data bases include:
Resource Records (RR) which define the mapping between names and addresses. The following
five types of RRs are most common.
Address Records (A) the name to address record which tells you that is
One name can point to several different IPs which can be useful when running a web service and
there is a need to load balance. (IN means that it is defining an internet address.)
Canonical Name Records (CNAME) is a way of defining aliases for a name. eg if the FTP server
is sooty but we want it accessible as, the CNAME record allows this.
It is best not to have a CNAME pointing to another CNAME but to an A name.
Mail Exchange Records (MX) used for e-mails. The local mail server has to find the identity of the
machine that handles mail for that domain, so takes everything to the right of the @ sign and looks
up the MX record for that address.
The extra number specifies the order of preference. Useful to have a backup mail server.
Nameserver Records (NS) used to delegate the responsibility of looking after part of the domain
to some other DNS.
Reverse Mapping Records (PTR) used to take an address and map it onto a name. To look up
the name that corresponds with the address, you reverse the order of the numbers and
put on the end. So in the DNS configuration file there would need to be
There are other RRs but they are not generally used including HINFO.
For IPv6 there is a different RR, the AAAA record.
Reverse addressing with IPv6 use the instead of and separate numbers by
dots instead of colons IN
PTR (all on one line)
$ORIGIN used to simplify writing IPv6 IPs. $ORIGIN used to define a string of numbers which
are then added to all numbers that follow unless they are followed by a dot.
Document Object Model. See XML
On an NT network, a collection of computers with a common account
database. The account database resides on a server called a Domain Controller. In W2K and later
releases, Active Directory works by creating domains within a company. A domain is defined by a
security boundary, and can span several physical sites.
-Domain Controller
A .net Server operating system responsible for controlling a local
A Windows server responsible for controlling a local domain.
-Domain Registries
and Win3.1 can only use 64MB of memory.
.COM files executed before .EXE files.
Too many files in a directory can slow performance, keep to less than 150.
dir switches,
/o:n the /o:n is a switch to order the files by name.
/p pauses the screen until a key is pressed.
/w displays the list in wide format.
/o:d displays files in order of date.
TREE all directories and files on the disk are displayed; switches
(vert. line) MORE displays the tree one screen at a time until a key is pressed.
/f scrolls directories and all its files.
Including a specific filename after the CHKDSK command checks that particular files for
CHKDSK has two switches;
/F fixes the lost units and gives the opportunity to save each to a file for examination.
/V displays the name of each file in every directory checked on the disk.
Only run CHKDSK from DOS or it can corrupt files.
CHKDSK will report but not fix cross linked files.
To direct the output of CHKDSK to a file named INFO.TXT, type
To run SCANDISK type HELP SCANDISK at the command prompt.
XCOPY32 enables long file names to be copied. Useful for copying one hard drive to another.
eg.xcopy c:\*.* /e/h/k/r d: where d: is the drive letter of the new disk
To boot up into DOS instead of windows. From a DOS prompt type atrib -s -h msdos.sys and then
edit msdos.sys. Look for the line that says BootGUI=1 and change the 1 to a 0. Finally save the
file. The system will now boot to a C prompt whenever you start up. Then type win to start
windows 95.
List of DOS commands available in Win95 Resource kit. Look for Win95rk.hlp file in the
Admin/Reskit/Helpfile directory. Open using Explorer.
DOS from Windows.
The configuration files used when you restart Win95 in MS-DOS mode are determined by the
properties of the 'Exit to MS-DOS' shortcut in the Windows folder. Locate using explorer, right
click and choose Properties. Click program tab and click Advanced button. If 'Use current
configuration' is selected, Windows will run the file dosstart.bat (in the windows folder) when dos
starts. If 'Specify a new MS-DOS configuration' then you can create a new config.sys and
autoexec.bat files for MS-DOS mode.
generates a directory list of file names and sends it to your printer.
PROMPT=$p$g defines the appearance of the DOS prompt. By default you get the current drive
and a greater than sign. $p adds the current directory path
-DOS Commands
ipconfig /?
ping /?
route print
tracert url or IP
Accessed through the command prompt.
ip configuration
provides available routes from your machine.
short for Trace Route. Traces the route to another system
Dynamic Random Access Memory.
-Driver files
Located in C:\windows\system, and c:\windows\inf, and
c:\windows\help files. Copy all into a new folder c:\drivers. Can reinstall all drivers from this
Digital Rights Management. Protects ownership, privacy, owners as
content travels from creator to distributor to consumer.
Distance Selling Directive. A retailer must provide the following
details before a sale: seller identity, price of goods, delivery costs, arrangements for payment and
delivery. After the sale the retailer must provide written confirmation of the order. Still have 7 days
to change your mind, cancel the order, and send it back. If the retailer fails to provide written
information on terms and conditions then you have 3 months to return the goods, but everything
must be returned unused. If the goods do not work the supplier legally has to offer you a full refund
and take the faulty goods back at no further cost to you. In the case of any return of goods the
money must be refunded within 30 days. The directive also states that consumers can cancel credit
card payments and be fully refunded by the card issuer, in case of fraudulent use.
Direct Stream Digital encoding - used on SACD
Dynamic Systems Initiative - from Microsoft
Downloadable Sounds Level 2
Digital Subscriber Line. Uses the existing copper cables to transmit
data. SDSL has the same up-link and down link speeds. ADSL often has a 512Kbps downlink and
a 256Kbps up-link speed. ADSL transmits data at a high frequency above the normal frequency
band of speech. Speech and Data can therefore go down the same line at the same time. The ANSI
standard for ADSL uses Discrete Multi-Tone (DMT) a type of frequency division multiplexing.
DMT takes the high frequency part of the line and divides it up into 247 channels, each 4kHz wide.
These are known as Tones. The system monitors each channel and shifts the signal between
channels to get the best signal for transmission and reception. Specific equipment needed for this.
On the Telco side a DSL Access Multiplexer (DSLAM) takes all incoming connections and sends
them on a pipe to the Internet. For DSL the cable is not shared unlike the system used by cable
companies which do share. At the client end an DSL modem is needed which combines a splitter to
allow voice as well as data.
-DSO Exploits
Data Source Object Exploits. Tracking software. Often the registry
entries for such tracking is not corrected by programs like Spybot. To change the registry entries
find the path from Spybot. Typical might be:
After opening zones and clicking on ‘0’ look in the right window, under ‘name’ is the key ‘1004’
and the type is REG_SZ. Right click and delete this REG_SZ value. Then tight click and create a
new DWORD Value, name it 1004. Right click on this new DWORD Value and goto modify.
With protection removed (default) the DWORD Value is 0. With protection applied the value
should be set to a Hex value of 3 (preffered). To be prompted, the value could be set to hex value 1.
It may also be necessary to do the same for key 1001.
Document Style Semantics and Specification Language. Modern
version of SGML.
Data Service Unit
Digital Transmission Content Protection over Internet Protocol - an
alternative to DRM.
Document Type Definition - a set of rules for tag syntax.
Data terminal equipment. Computers and terminals are examples.
Disaster Tolerant Disk System. Data distributed in different physical
Dual-Tone Multiple Frequency. The audio signalling frequency on
touchtone phones.
Digital Terrestrial Television
Dial Up Networking.
Digital Video. European PAL resolution - 720x576.
Digital Versatile Disk. RAM disks store 4.37GB (not 4.7GB) on a
single side and 9.4GB double sided. The spin speed of a DVD is much lower than that of a CD but
a 6 speed DVD achieves about the same sustained data transfer rate as a 32 speed CD ROM.
DVD tweak sites
Dual layered DVDs known as DVD9, single layered DVDs known as DVD5
The pits of DVDs are spaced 740nm apart.
Also see CLPV and CLEV
The specification was released in March 1999. Uses a sample size of
24 bits and a sample rate of 192kHz. Can record an audio signal with a frequency range of 0 to
96kHz and a dynamic range of 144dB. Can store up to 17Gbytes of data on a double sided dual
layer disk and can have up to 6 audio channels. Uses a PCM system. (Cf a CD, 16bit, 44.1kHz
sample rate, recording 5 to 20kHz with a dynamic range of 96dB on a 650MB disk)
Digital Video Interface. Replaces the RGB socket allowing flat
panels and projectors to be connected. There is no conversion loss between analogue and digital so
picture is better. Delivers a digital signal from the graphics card to the monitor
Dense Wavelength Division Multiplexing. The use of additional
wavelengths of laser light (different frequencies) adds extra capacity on the cable without having to
change the cable. Current technology supports up to 240 simultaneous channels. DWDM is bit-rate
and protocol independent.
Uses temperature-controlled distributed feedback (DFB) lasers and have extremely tight channel
spacing of 0.4 or 0.8nm.
Extensible Authentication Protocol
Electronic Attack Response Group. Part of UNIRAS. Provides direct
assistance to government departments experiencing an electronic attack.
-Easter Eggs
A hidden program within a main application.
Excel 97. New workbook select Edit, GoTo and type X97:L97 in the Reference field and click
Enter. press the Tab key and then Ctrl, Shift and click the Chart Wizard button in the toolbar.
Animated landscape - left mouse button forward and right on backwards. A stone pyramid is there
with the credits of the programs writers. Esc returns top the worksheet.
See Digital Telephony
European Convention of Human Rights.
An open source initiative aiming to provide a supplier-neutral
software development platform. was formed in 2001 by IBM, Borland, Merant, Red
Hat, SuSE and others. In 2004 Eclipse became a not for profit corporation. It is written in Java and
comes with plug-in construction toolkits.
Enterprise Content Management
Extended Capabilities Port. An improved parallel port which
transfers data at over 2MBps and is bi-directional in operation. ECP mode primarily designed for
devices such as ZIP drives.
Extended Data Availability and Protection. Now emphasised by RAB
Enhanced Data GSM Environment.
Electronic Data Interchange.
Extended Data Out. To read a word of computer memory it must be
precharged first. EDO memory speeds up this sequence by precharging the next word while still
reading the current word.
Extensible Firmware Interface. Intel's replacement for BIOS.
Ethermet in the First Mile Alliance. Connections to WANs and the
Encrypting File System. W2000 and XP Pro - encrypts the whole
hard disk.
Electronic Fund Transfer.
Electronics Industries Association. An USA trade organisation that
issues its own standards and contributes to ANSI; developed RS232 and EIA-568, a much used
building wiring standard.
-EIA 485
Specifies the electrical characteristics of generators and receivers for
use in balanced digital multiport systems
-EIA 568A
Colour code for 10Base-T.
European Institute for Computer Antivirus Research. Antivirus
programs should be able to detect the following file as a virus, when saved as
Enhanced Integrated Drive Electronics. This describes the electronics
used to run large hard drives on modern computers. Also known as Fast ATA or High Performance
ATA. An EIDE controller can handle up to four hard drives etc at a time. Enhanced IDE faster
than IDE and allows disks larger than 528MB to be directly accessed. Max disk size 8.4GB,
transfer rates up to 16MB/s and four drives can be connected to one adaptor. See UDMA
Enterprise Instant Messaging
Extended ISA slots. 32 bit slot running at 8MHz.
Equal Level Far End Cross Talk.
Servers and mail readers only need to be able to handle messages of
up to 60KB. E-mail disclaimer: To alert the recipient that the e-mail may not be the whole story.
Should inform recipients that e-mails may be monitored or stored. (Issue of personal e-mails)
Should be at the top of all e-mails not bottom. Should say that contracts can only be concluded in
Should disclaim liability from acts or opinions that the company would not have sanctioned.
(In printing) Enhanced Meta File
Expanded Memory Manager. A utility allowing DOS programs to
access memory above the 1MB limit that constrained earlier versions of DOS. The most common
example is EMM386, included with DOS 5.0 and above. Windows 95/98 have built in memory
management and don't need EMM.
Or smiley is a set of keyboard characters used in e-mails to denote
joking, sarcasm etc. eg :( indicates a joke, :) unhappiness.
Enhanced Messaging Service.
Coding information in a way that makes it difficult to decode without
either a key (cipher) or an awful lot of mathematical muscle. The longer the length of the cipher (in
bits), the more difficult it will be to break.
Two main types, symmetrical and asymmetrical.
Symmetrical uses the same cipher to encrypt and decrypt data. Methods are based on mathematical
algorithms. One of the first (mid 1970s) was the Data Encryption Standard (DES), an encryption
algorithm using a 56 bit cipher. DES was at one time considered strong enough to be used for
banks' automatic teller machines, but as computer power has increase it was replaced by triple DES,
which ran the same piece of data through the DES algorithm three times for extra strength.
Towards the end of the 1980s, a new encryption standard called AES (Advanced Encryption
Standard) was developed and was established in 2001.
Symmetric encryption has the problem of getting the cipher securely to the other person. This is
where asymmetric or Public Key Encryption (PKE) comes in. PKE uses two keys: a private one and
a public one. If one key is used to encrypt, the other will decrypt. If A wants to send a message to
B, it uses B's public key (which is available to everyone), to encrypt the message. Once it is
encrypted, the only thing that can decrypt the message is B's private key, to which only it has access.
The original developers of this technology formed RSA Security.
Symmetric key encryption is always faster than asymmetric. Whereas AES uses a minimum cipher
length of 128 bits, the RSA algorithm starts at 1024 bits.
An alternative to the RSA algorithm is elliptical curve cryptography, which works with 160 bits and
can be a useful form of asymmetrical key encryption on resource constrained devices such as PDAs
and smart phones.
Digital signatures provide a way of enabling people to "sign" their ciphers and messages in order to
validate that the message is from who it says it is. Company A creates its digital signatures using its
private keys. As before, it encrypts the message that it wants to send using a symmetrical algorithm
(quicker than asymmetric one), and then encrypts the cipher for the message using B's public key.
But then it also runs the unencrypted message through a mathematical algorithm called a hashing
function, which produces a unique short string of characters. It then encrypts this string (known as a
hash) with its own private key. Everything is then sent to B.
B then uses its private key to decrypt the symmetrical cipher, which it then uses to decrypt A's
message. But it then uses A's public key to decrypt the hash string. It runs the decrypted message
through the same algorithm that A used to create the hash. If B's hash matches A's then it knows
two things: first that the message has not been tampered with en route. Second, that the message
definitely came from A because it was decrypted using A's public key, which means it must have
been encrypted using its private key.
Hashing algorithms come in various forms: MD5 is still used in many systems. SHA-1, created by
the National Security Agency in the mid 1990s has largely superseded MD5.
PKE had a major challenge, which was to verify that people's private and public keys were not
being created fraudulently. Trusted certificate authorities (e.g. Verisign) were set up to help govern
the creation of keys in what became known as Public Key Infrastructures (PKIs). Within a PKI, a
certificate authority would create and sign company A's key to verify it. Take up was slow and
difficult to use.
To counter this PKI advocates often quote public key technologies such as Secure Socket Layer
(SSL) or its successor, Transport Layer Security (TSL), which provides the padlock icon seen in
secure browser sessions. These require no authentication of the user, but were there simply to
authenticate the server and secure transactions.
PGP, an open public key encryption software tool developed in 1991 by Phil Zimmerman. PGP is
significant because it offered an alternative to top down certificate authority model used in PKI. For
PGP, certificate authorities are replaced by trusted individuals, who endorse other peoples keys by
signing them, leading to the phenomenon of key-signing parties.
-Enterprise network
Up to 500 users
Electronic Programme Guide. Lists programs on TV and enables
complex recordings to be made
Explicitly Parallel Instruction Computing - as used on Intel's 64-bit
Itanium family
An operating system for mobile devices including phones developed
by a consortium of companies (Psion, Phillips, Nokia, Matsushita). It goes further than WAP in
offering colour graphics, sound and rich text. It also allows developers to design their own
interfaces unlike the rival Windows CE.
Enhanced Parallel Port. Data transfers of 2MBps and bi-directional.
Used mainly by printer monitoring software.
Eligibility Requirements Dispute Resolution Policy
Employee Relationship Management
Enterprise Rights Management. Software which allows organisations
to establish and enforce policies regarding who can do what with electronic messages and enterprise
Enterprise Resource Planning
Extended Service Set ID - effectively the name for WLANs
An IEEE standard developed first by Xerox and then sponsored by
Xerox, Intel and DEC. Does not matter whether it is arranged as a Star or a Bus. Uses CSMA/CD
as the data transmission protocol. Ethernet only has a useful capacity of 45% utilisation and a
theoretical limit of 60%.
Developed at Xerox Parc by Bob Metcalfe and David Boggs in 1973. Metcalfe was looking for a
way to connect Xerox's Alto PC to a printer and came up with a cabling infrastructure that enabled
multiple devices to be connected and new devices added on a single wire. In 1976 Metcalfe
published Ethernet: Distributed Packet Switching for Local Computer Networks
Originally devised by Bob Metcalfe at the Xerox Palo Alto research centre. Originally ran at
2.94Mbps but later (1983) internationally defined as the 10Mbps 802.3 standard. Conceived as a
technology to join together multiple computers over a shared medium. Originally done using
10base 2 coaxial cabling - 50 ohm coaxial cable. Multiple stations transmitting at the same time
cause collisions. To avoid this, Ethernet uses a Carrier Sense Multiple Access/Collision Detection
(CSMA/CD) algorithm.
Later Metcalfe left Xerox in 1979 and formed 3Com.
In 1997, the IEEE finalised the 802.3u standard which is the 100Base-T standard or fast Ethernet.
1998, the IEEE defines the standard for gigabit Ethernet over fibre.
2002, the standard for 10Gb Ethernet is expected to be ratified.
CSMA is used to detect when the medium is free. When it is, a station will transmit. If the medium
is busy then it waits for it to become free. There are two main algorithms to perform this: 1persistent CSMA and non-resistant CSMA. The 1-persistent CSMA monitors the channel until it is
free. It is called 1-persistent because a station will transmit with a probability of 1 when the channel
is free. If a lot of stations are waiting then a collision will occur the moment the line is free. This
means that collisions are more likely when the load is high. Non-resistant CSMA waits for the line
to become free and then waits an additional random amount of time before transmitting. This is
slower than 1-persistent but more efficient at high loads. Ethernet used the 1-persistent model. So
when collisions happen because of two stations transmitting at the same time, both transmitting
stations stop and wait a random amount of time before starting to transmit again. The random time
interval ensures that the same collision does not happen repeatedly.
Collision detection has three main concepts: collision window, frame size and collision back-off.
The collision window specifies the amount of time that a transmission is vulnerable to collisions
after the transmission has started. Caused by the physical distance between the machines and the
speed of electrical or light transmission. Consider two machines, A and B, on a long cable. If
machine A starts transmitting, there will be a delay before the signal will hit machine B. If this
delay is sufficiently long that machine B decides that the channel is free and so starts transmitting
then a collision will occur.
Frame size: As a station is barred from transmitting when another is already transmitting, Ethernet
defines a maximum transmission size of 1518 bytes on all frames transmitted. There is also a
minimum frame size of 64 bytes in order to ensure that there is always time for a station to detect a
collision before it finishes transmitting. After transmission all stations have to remain silent for
9.6ms. This interpacket gap is used to allow circuits to recover and reset in time for the next
Collision back-off: when a collision is detected, the transmitting station 'floods' the network. This
ensures that all systems on a segment detect the collision.
The 802.3 Ethernet frame format is shown in the diagram below.
1 2 or 6
2 or 6
destination source
start of delimiter
length of data field
0 - 1500
0 - 46
Preamble: the seven byte field contains the pattern 10101010 seven times. It produces a 10MHz
square wave in the Manchester Biphase encoding scheme, which is used to physically put data on
the wire. This information is sued to synchronise the receiving station with the transmitting one.
Start of frame delimiter: Defines the actual start of the frame. It contains eight bits transmitting the
pattern 10101011.
Destination and Source addresses: These are either two or six bytes long (16 or 48 bits). The
destination address is looked at by all receiving stations. If the destination address does not match
the local settings, the frame is discarded. The source address is used so that replies can be sent
back. There are two standard lengths for Ethernet addresses, though the industry has mainly settled
on the 48 bit standard. This is usually known as the Medium Access Control (MAC) address, which
is hardwired into the NICs. Usually represented by six hex numbers e.g. 00 FD 4D 43 23 87
Length of data: Defines the length of the data in a packet. Minimum value of 0 and a maximum
value of 1500. Because the Ethernet standard states that the minimum length of a packet must be at
least 64 bytes long, including all of the other components in the frame, this means that the minimum
length of the data field has to be at least 46 bytes. (See Pad below)
Data: This field can be from 0 to 1500 bytes long. It contains the actual data that is being
transmitted. When an IP frame is being sent over an Ethernet network, it is stored in this portion of
the frame.
Pad: This is used to push the size of the frame up to the minimum length of 64 bytes if the data
field is not long enough.
Checksum: This four-byte field contains a checksum for the Ethernet package. It allows the
receiving station to check that the contents of the frame have not been damaged in transmission.
IP on Ethernet: Devices sitting on an Ethernet network only understand Ethernet addresses. For IP
to work in an environment such as this there has to be a method of finding out which IP address
belongs to which Ethernet address. This is the task of ARP or Address Resolution Protocol.
Study the way humans relate with technology
European Telecommunications Standards Institute
Ethernet Virtual Network.
-Even parity
Data verification method in which each character must have an even
number of "1" bits
-Executable code
The compiled and linked version of the object code. Contains all that
is required to execute it within the operating environment.
A standard way of including extra information about an image with
the file for a camera.
-Extended Memory
Any memory beyond the 1MB of the original PCs. Also known as
Used to extract files from CAB files on Windows CDs. The extract
command searches all the consecutively numbered cabinet files starting with the one you specify. It
is not necessary to know which cabinet file contains the file to be restored.
extract /A win 9x_??.cab filename.ext /L c:\location to which it is to be restored. ??.cab is the
lowest numbered .cab file
A web site that is a closed community protected by a password and/or
firewalls. It is typically provided by businesses for suppliers, key customers etc.
-Fast ATA-2
A hard drive standard that transfers up to 16.6MB/s. Also
incorporates modes as IDE Mode 4 and Multiword DMA Mode 2.
File Allocation Table. This is a feature of the MS-DOS operating
system that keeps track of what's where on disks. This is the only means DOS can use to find data
on a disk. DOS doesn't necessarily store programs and data in consecutive chunks on the disk,
instead taking the next available cluster. It is the FAT that maintains the link addresses for
subsequent but physically separated clusters. Using 16bit addresses it can only support disks up to
2GB. FAT 32 uses 32 bit addressing and supports hard disks up to 2TB.
-Fatal exception
Generated by the Windows operating system when it detects invalid
code, invalid data or illegal instructions being accessed by a program. Generally requires a restart to
clear it.
-Fatal exception OE
Usually occur when Win95/98 encounters errors in the Registry.
Fastest fax speed is 14.4kbps but most work at 9.6kbps.
Fibre Channel Arbitrated Loop. A high performance drive interface,
as used by high end SCSI drives. Data transfer rates of up to 200MB/s are supported. A storage
protocol based on Token Ring and FDDI.
Fibre Channel Industry Association
Fibre Channel over IP. A SAN interconnect protocol
Flip Chip Pin Grid Array. Used on later PIIIs The flip chip
designation referred to the fact that the processor core is situated at the top rather than the bottom of
the chip
Fibre Channel Physical Layer
Fibre Channel SCSI. Used on SANS.
Fibre Distributed Data Interface. A token passing ring
network specification developed by ANSI, implementing dual optical fibre rings.
Run from floppy. First option is to 'Create a DOS partition or logical
DOS drive'. Select Yes. Then 'Create Primary DOS Partition'. Usual to choose maximum space
available. After the message 'Primary DOS Partition created' appears use Esc to return to main
menu. Select 'Create extended DOS Partition' and then 'Create Logical DOS Drive(s) in the
Extended DOS Partition'. Fdisk supplies the corresponding values until the entire hard drive has
been assigned. Use ESC to return to main menu and choose 'Set active partition'. Select the
primary partition, which now becomes the C drive. Press ESC twice to exit Fdisk.
-Fdisk/MBR, sys c:
To Fdisk the Master boot Region of a hard disk?
Fixed Disk Parameter Table.
Full Duplex. Simultaneous, two way, independent transmission in
both directions.
Forward Error Correction.. A mathematical method of encoding data
so that errors can be detected and corrected on receipt. It is unidirectional, i.e. there is no need for
feedback from receiver to transmitter to indicate errors or request re transmission - the decoder in
the receiver performs all detection and correction.
Federal Computer Incident Response Centre. Monitors malicious
attacks on federal systems.
Federation of the Electronics Industry
Far End Cross Talk
Frequency Hopping Spread Spectrum
-Fibre Channel
Used with Storage Area Networks (SANs). It is a combination of
other standards including FDDI, SCSI, HIPPI and IPI. Offers the best of Channels (point to point)
and networks (an aggregation of hosts) through the Fabric. Hosts only have to monitor their own
point to point connection to the Fabric. This reduces the overhead placed on the host and allows
transfer speeds of up to 2Gbps.
Fibre Channel offers a fast and reliable transmission platform. A single mode fibre and longwave
light source allows data to be transmitted 10km at 1Gbps.
The protocol is defined in a similar way to the OSI 7-layer model, though Fibre Channel only has
five layers.
common services
framing protocol/flow control
FC-0 layer - provides the physical link including the fibre, connectors etc
FC-1 layer - defines the transmission protocol. It is responsible for serial transmission and
encoding and decoding data. The system is similar to FDDI but uses a 10-bit transmission code as
opposed to the 5-bit code used by FDDI. Data is encoded 8-bits at a time into the transmission
character. Some redundancy allows some recovery in the event of an error.
FC-2 layer - Defines the frame layout and header formats and serves as the transport mechanism.
The layer is made up of a set of building blocks used to transfer data across a link. These are:
Ordered Sets - are 4-byte transmission words that have a special meaning, e.g. start and end
of frame delimiters, Idle (node ready for transmission and reception) and Receiver Ready (interface
buffer can accept more frames.
Frames - used to contain the data transmitted and have a max. length of 2048 bytes. Frames
can also be used to send messages including acknowledgements and rejections. The Fabric has to
accept frames from the source port and route them to the destination port. This layer is also
responsible for splitting the data into frames and reassembling them at the other end.
Sequence - a collection of related frames in transmission. Each frame is labelled with a
unique sequence number so that they can be reassembled in the correct order at the destination end.
Also used for error control to make sure that all of the data has arrived.
Exchange - one or more sequences for a single operation. Can be uni or bi directional, but
only one sequence can be in operation at a time.
Protocol - defines the service offered. Includes Fabric logon and data transfer.
Flow Control - Part of the job of this layer is to provide adequate flow control. Achieved
by sending control frames. When a receiver's buffer is full, a Busy frame is sent over the network.
This causes the transmitter to back off until the receiver is ready.
Service classes - Three possible. Circuit switching with guaranteed delivery in order which is used
by data channels: Packet switching with guaranteed delivery. Packet switching without
guaranteed delivery.
FC-3 layer - provides common features for advanced features including:
Striping - this multiplies bandwidth by using multiple ports in a large pipe
Hunt groups - allows multiple ports to respond to the same alias address.
Multicast - lets one transmission be delivered to multiple addresses.
FC-4 layer - Defines the application interfaces that can be run. The list of supported protocols
A special network card has to be installed into the host and gives the host a physical address and
allows them to hook into the fabric. Hosts include servers, clients, tape libraries, disk drive arrays
etc. Once a client machine connects to the Fabric it can access storage on any other machine subject
to permissions. These can be placed many kilometres apart and so some could be effectively off site
-Fibre Optic Cables
Tube and Tight Buffer.
Cables containing optical fibres. Two main types; Loose
Column in a database table.
-File associations
To associate a file Hold down Shift and then right click. Select Open
With. etc
-File extensions
Batch file
Help content files
.gid Global index files created by Win95 Help program
.pps Microsoft Power Point
Outlook files
.syd Backup file when changes made using Sysedit
To open a pre-registered file with a different program - right click while holding the shift key.
Select open with then click Always Use this Program to open these files.
List of extensions at
Extensions to delete:
any files older than a day.
*.Backup files created by Windows
Temporary word files left after a crash.
Backup files from various applications
Installation files
Files created by scan disk and chkdsk
Windows will create these if it needs them.
Windows will create these if it needs them
Log files delete if more than a few days old
Old versions of files
Log files created by past Windows boots.
Scrap objects - temporary files created in OLE supporting applications
Temporary files
Word backup files.
-File Server
-File type
Stores files for users but does no processing.
Three letter extension to the file name. To change a file type's
association open Windows explorer and right click a file of the type you want to change. Right
click the file and select Properties. Note the Type, click OK. Now select View, Option, and click
the File Types tab. An alphabetical list of Registered file types on the computer is shown. Double
click the file type to be changed (noted earlier). The Edit file Type dialog box appears and in the
Actions list double click Open. Another Dialogue box appears. In the 'Application used to perform
action' field, enter the path and filename (enclosed in quotes) of the application you want the file to
be opened in. Use the Browse button to find the full path. Click OK. Click Close a couple of
To associate a file type with more than one application, before clicking Close, in the File Type
dialog box, click the New button. A small dialogue box appears for adding another action to the file
type. In the Action field, type an easily recognised name for the new application. In the
'Application used to perform action' field enter the program's path and file name. Click OK or Close
until reaching the desktop. If a file is right clicked a choice is available as to what to launch the
application with.
-File virus
Infects program (exe and com) files. Each time the program is run it
copies itself.
A system designed to prevent unauthorised access to a network,
particularly from hackers. All information entering or leaving a network is scrutinised, and rejected
if it fails to meet security criteria.
The first commercial firewall product was DEC's Secure External Access Link, released in 1991.
Others quickly followed but the market took off in 1994 with Checkpoint's Firewall-1, the first
product with a simplified icon and mouse user interface.
High speed applications bus. Also known as IEEE-1394. Can
transfer up to 400Mbps and supports plug and play and is hot swappable. Can support up to 63
devices. Defined speeds of 100, 200 and 300Mbps. Asynchronous and isochronous data transfer
allowed, isochronous being the fastest.
The cable consists of two twisted pairs which carry the data and control signals and twin power
lines. The wire can supply up to 1.5A at anything from 8 to 40V.
Can be daisy chained and can have up to 16 on a chain. Can use Firewire nodes to create another
three chains from one chain so can have in theory 65,536 nodes in a complete network.
ID numbers and resources automatically assigned when device connected and released when device
disconnected. A Firewire system can work independently of a PC (unlike USB).
Originally introduced in 1995 and developed by Apple. In 2003 a new standard was ratified IEEE1394b which is dubbed Firewire 800 and offers transfer speeds of up to 800Mb/s
A computer program or software stored permanently in ROM.
An authoring application for web sites. Based on SWF (Shockwave
for Flash file format) a web optimised, vector based format. Describes the difference between
image frames to enable smooth animations.
-Flat file database
All of the data is stored in a single table.
Fixed-Mobile Convergence. The basic premise is that people should
be able to have a single mobile handset or smart phone to replace a separate desktop and mobile
phone. The device should be able to make both VoIP and data calls via the private branch
exchanges that route local calls within offices and out onto the PSTN, as well as mobile cellular
-FM Synthesis
Frequency Modulation Synthesis is a cheap but very reliable means of
producing sounds on a PC, but any music does tend to sound artificial. Wavetable synthesis gives
much better reproduction.
Freedom Of Information Act
Fax over IP
Fibre Optic Inter Repeater Link - Ethernets standard fibre link.
Fibre MAUs
True Type fonts (TT) needed by Windows, Arial, Courier New,
Symbol, Times New Roman, Wingdings, Comic sans, Impact, Verdana, and Tahoma in all their
Dialog boxes, menus etc use bitmap fonts (A icon) need Courier, MS Sans Serif, MS Serif, Small
fonts and Symbol.
Domains in Active Directory can be structured into hierarchies called
Trees. A forest is a collection of domain trees. Ideally it will cover a whole company.
Formats disks. Adding the /S switch tells format to make the disk
bootable and install system files.
-Formatted Capacity
This is the usable size of the hard drive. It is about 15% less than the
unformatted capacity. The space is used by the system to map out the usable areas and for
managing the data.
-Form Factor
The physical size of a drive. Common sizes are low profile (LP), half
height (HH) and full height (FH).
Gives a user-friendly view of the data held in a database table
Designed by IBM in 1957 - could do complex calculations but could
not process data or text.
-Foveon X3 Image Sensor
Features three separate layers of photodetectors embedded in silicon. The silicon absorbs different
wavelengths of light at different depths, so each layer captures a different colour. This is the only
type of image sensor to capture red, green and blue light at every pixel location.
Ferroelectric RAM. Made by Ramtron. A non volatile memory
capable of replacing serial EEPROMs but with lower current consumption. Has an unlimited
number of read/write cycles. Is faster to program than EEPROMs.
-Frame Relay
Packet-switched network similar to X25, but with end-to-end error
checking and high speed transmission rates.
Failure Resistant Disk System. Often implemented through RAID
Full Screen Anti Aliasing
Front Side Bus. The bus that the processor uses to communicate with
the rest of the computer, in particular the main memory.
Free Space Optics. It is capable of gigabit data rates but is restricted
to true line of sight links at distances of between 2-3km. Its real deficiency isits poor performance
in extreme weather conditions, eg fog, heavy rain etc.
Failure Tolerant Disk System. Looks to duplicate controllers as well
as disks.
Foil Twisted Pair cables
File Transfer Protocol. Used to copy programs often to an ISP.
Details on how to do this for Demon on Common FTP
programs include CuteFTP, FTPWolf and BullteproofFTP.
FTP - anonymous login - accept 'anonymous' or 'guest' as an ID and usually any word ending with
an @ symbol as a password. Considered polite to login with your e-mail address.
Archie an FTP search engine invented in 1992. lists of ftp files. To add to the Demon ftp archive
Company ftp site list
FTP has a well defined port number (21), but this is only used for control messages. When a file is
downloaded, the FTP server negotiates with the client a higher port number for the transfer to take
place on. This means that often a large number of ports have to be left open.
Much older than HTTP – first referenced in April 1971 whereas HTTP only appears in May 1996.
FTP designed as a two way protocol for moving large files, whereas HTTP designed for pulling lots
of small files from a server
-Full Height
Full height drives are 3.25" tall.
-Function Keys
rename a selected file or folder
to send a file or sub folder
displays the combo box in Explorer
refresh the screen
to switch panes in Windows Explorer
for special boot menu options like safe mode
for menu access
Speech compression algorithm used with H.323 in VoIP. Requires
64Kbps bandwidth. Needs end to end delay values of 200-300ms and packet loss levels of 2-3%
Speech compression algorithm used in VoIP. It combines small
packet sizes with the voice quality of G711 and delivers a transmission rate of 8Kbps. Requires less
that 150 - 200ms for packet loss values of 1-2%
Generic Access Profile
Generally Accepted Accounting Principles - to be replaced with IAS
A computer system in one network which allows access to another
network, by transmitting the data in the protocol of the receiving device.
Global Catalogue - part of Active Directory.
Graphical Device Interface. The PC does all of the processing and
translating when printing a document from Windows using a laser printer.
Global Grid Forum - Grid Computing
Graphical Interchange Format. Invented by Compuserve. A
compression technique, more effective with logos and banners than pictures. Only supports 256
colours. GIF images have the ability to be interlaced so that the image can be downloaded in stages.
The GIF image format uses a built-in LZW compression algorithm. This compression algorithm is
patented technology and currently owned by Unisys Corporation. In 1995 Unisys decided that
commercial vendors, whose products use the GIF LZW compression, must license its use from
UNISYS. End users, online services, and non-profit organisations do not pay this royalty. Since it's
inception GIF had been a royalty-free format. To avoid this royalty, vendors have developed an
alternative to GIF that supports transparency and interlacing called PNG ("ping"), the Portable
Network Graphic.
GIF87a was released in 1987. GI87a allowed for the following features:LZW compressed images
multiple images encoded within a single files
positioning of the images on a logical screen area
So it was possible to do simple animation with GIFs by encoding multiple images, "frames", in a
single file. GIF89a is an extension of the 87a spec. GIF89a added:
how many 100ths of a second to wait before displaying the next frame
wait for user input
specify transparent collar
include unprintable comments
display lines of text
indicate how the frame should be removed after it has been displayed
application-specific extensions encoded inside the file
Most browsers support single image GIF87a and will recognise the transparency flag of GIF89a and
nothing else. All transparent GIFs are GIF89a format.
GIF89a is still a 256-colour (maximum) format. GIF allows for any number of colour between 2
and 256. The fewer colours the less data and the smaller the graphic files. If your GIF only uses 4
colours, you can reduce the palette to only 2 bits (4 colour) and decrease the file size by upwards of
The Structure of a GIF89a file.
GIFs are composed of Blocks and Extensions. Blocks can be classified into three groups:
Special Purpose
Control blocks, such as the Header, the Logical Screen Descriptor, the Graphic Control Extension
and the Trailer, control how the graphic data is handled. Graphic-Rendering blocks such as the
Image Descriptor and the Plain Text Extension contain data used to render a graphic. Special
Purpose blocks such as the Comment Extension and the Application Extension are not used by GIF
decoders at all. The Logical Screen Descriptor and the Global Colour Table affect all the images in
a single file. Each Control block will only affect a single Image block that immediately follows it.
GIF89a File Structure.
may include an optional GLOBAL COLOUR TABLE (99.5% of the time this will be
a stream of graphics (each graphic being composed of the following)
an optional GRAPHIC CONTROL BLOCK (one preceding each IMAGE)
which can include an optional LOCAL COLOUR TABLE for an image
and the actual IMAGE or TEXT data table
GIF TRAILER ends the series of images
COMMENT BLOCKS may appear anywhere as they are ignored. (Do NOT place them before the
Netscape Looping Extension!!)
The HEADER block is a small 6-byte (6-character) block. It is the first block in every file and
contains the GIF version of the file (i.e. either GIF87a or GIF89a). GIF image decoders use this
information to determine the version of the file.
The LOGICAL SCREEN DESCRIPTOR is always the second block in a file. It defines an area of
pixels which you can think of as a screen (like a projector screen). The dimensions of this area
define the size of your GIF on screen. This information determines how much space is reserved onscreen in your browser to display the image. If your logical screen is larger than your image, you
will have space around the image when displayed. The logical screen area should be large enough
to display all of your individual frames in it. If an image in the GIF file is larger than the logical
screen or, by its positioning, extends beyond the screen, the portion that is off-screen will not be
The Logical Screen Block also chooses one of the colours in the Global Colour Table to be the
Background colour of the screen. This colour selection is ignored by Netscape Navigator. If a GIF's
background area shows through, Navigator displays the colour set in the BGCOLOR of the page's
body or, if none is specified, the background colour set in the menus under OPTIONS/GENERAL
PREFERENCES/COLORS. Now, of course, the question arises; how do I get it to be transparent?
Well, this SHOULDN'T work, but it does. Apparently, if Netscape's decoder finds a Control block
(it must be first, before any images) with Transparency turned on (any colour) the background of the
GIF will be transparent. This will allows background GIFs to fill in the logical screen background.
A GIF file contains a global palette of common colours for all the images in its file to work from.
(NOTE: It is technically possible for a GIF NOT to have a global palette, but this would be
extremely rare.) This palette can have 2, 4, 8, 16, 32, 64, 128 , or 256 defined colours. Palettes are
very important. Every colour displayed in your GIF must come from a palette. The fewer colours
used, the easier it will be for systems to display your images. The global palette is applied to all
images in a GIF file. If an individual images differs greatly from that global palette, it may have a
local palette that affects its colour ONLY. However, no image can ever reference more than one
palette, so 256 colours per image is the max. Having a bunch of local palettes with wildly varied
colours can sometimes cause colour shifts in your display. (It also probably indicates a gaudy mix of
The Logical Screen Header can also contain the aspect ratio of the image. This can sometimes
account for GIFs appearing stretched out or scrunched.
Netscape Navigator has an Application Extension Block that tells Navigator to loop the entire GIF
TABLE OF THE LOGICAL SCREEN DESCRIPTOR. Only Navigator 2.0 or better will recognise
this Extension block. The block is 19 bytes long composed of: (note: hexadecimal equivalent
supplied for programmers)
: 33 (hex 0x21) GIF Extension code
: 255 (hex 0xFF) Application Extension Label
: 11 (hex (0x0B) Length of Application Block
(eleven bytes of data to follow)
bytes 4 to 11 : "NETSCAPE"
bytes 12 to 14 : "2.0"
byte 15
: 3 (hex 0x03) Length of Data Sub-Block
(three bytes of data to follow)
byte 16
: 1 (hex 0x01)
bytes 17 to 18 : 0 to 65535, an unsigned integer in
lo-hi byte format. This indicate the
number of iterations the loop should
be executed.
bytes 19
: 0 (hex 0x00) a Data Sub-block Terminator.
The iteration count is ignored and the loop is infinite (an iteration count of zero indicates infinite). I
strongly suggest you code the count to be accurate, so that when iterations begin working your GIF
will not need to be modified. Technically that is all that needs to be done with this block.
A CONTROL BLOCK controls certain optional aspects of how an image is displayed. A Control
block only affect the image immediately following it. For this reason, you should never include any
block between a control block and the next image descriptor block. This Graphic Control Extension
if this image has a local palette of its own
if one of the colours in this image is transparent
if a user input is requested before proceeding
if a timed delay in 1/100ths of a second should be used before displaying THIS image.
what should be done with the image after it has been displayed (removal controls)
You should avoid using a local palette as it increases the likelihood of a confused video display. If a
local palette doesn't exist, the global one is used. One of these colour is designated as transparent in
the control block.
User input and timing work together. When an image is described, it is immediately rendered on
screen. Then, if a timed delay is set, it will wait for x/100ths of a second before removal and
proceeding onto the next image. If a User Input is specified, the image waits until the user strikes a
key, clicks a mouse or whatever. What is considered user input is determined by the program
displaying the GIF. If both options are elected, the image remains until the delay expires or a user
input occurs, whichever comes first.
Just before preceding to the next image, the removal options are performed. You may remove the
image by:
nothing: perform no action
leave as is: leave the image on screen, should be same as nothing in most cases
previous image: replace it with what was there before; this is difficult to implement and is
the most powerful choice.
background: replace with the logical screen background colour. (note: If Navigator detected
transparency, this will be replaced by the HTML specified background)
An IMAGE BLOCK contain (data) an actual image. This image can be any size and have a palette
of any size. You can have a mix of 16-colour, 2-colour, 256 colour, etc images in a single GIF. In
addition to the actual image table data you have the following:
the picture's size in pixels
the position of the image on the logical screen
whether it is interlaced
an optional local palette for this image
The image's size in pixels cannot be modified. It is determined by the data of the image. Changing
this would cause data corruption.
The top and left position of the images are within the defined logical screen. With this a small
bitmap of an object could be placed anywhere within the screen area, rather than create an entire
image with the object positioned within it.
Interlacing is a way of saving and displaying the image data. For interlacing to occur, the image
must be set to save interlaced. Interlacing is not turned by the browser. It may be ignored by the
browser. Interlacing saves alternate rows, producing a venetian blind or blocky-focusing effect,
depending upon how the browser handles interlacing. Interlacing stores the rows of the image in the
following order:
You can include comments in your GIF. These can be markers for long animation sequences or
statements of ownership.
In addition to images you can also render text on screen with a GIF. Unfortunately many programs
don't recognise the text.
The Trailer is simple. It indicates the end of the GIF file. It is unmodifiable and cannot be accessed
in anyway.
The block types and features contained in the animated GIF:
Dimensions (x,y)
Aspect ratio (0=1:1)
Global palette: Bit-depth (1-8) "Background colour" index (0-255) Sorted by frequency? (y/n)
Colour table
Repetitions (0-65535)
One per image
Transparent color index (0-255)
Delay (0-65535)
User input? (y/n)
Disposal method (0-3)
One or more
Dimensions (x,y)
Position (x,y)
Interlaced? (y/n)
Image description
Local palette? (y/n)
If present: Bit-depth (1-8) Sorted by frequency? (y/n) Color table
Search engine -
Searches for phrases - put into quote.
OR searches - include upper case OR
+ searches - words like and are ignored. If the word is essential include a + directly before the word
and a space after the word.
- searches - used when a word can have two meanings, e.g. bass - fish or music. Just to find the
music pages search for "bass -fish "
-Google site operators
Can be used to search out whole domains for specific words.
eg the query "site:edu test answers" would return a list of every .edu domain that possessed the
words "test" and "answers".
The site operator can also be used to map the contents of a target web server. The query
" scmagazine will return a list of every web page held by the web server bearing the words "sc magazine", which is all of them.
The operator "intitle:index.of parent directory," allows the directory listing and structure to be
obtained from the Google cached data.
The operator "filetype: " allows a particular type of document to be searched for specific words. eg
"filetype:pdf security"
The operator "link: " is used to search for sites with links to a specific site
The operator "cache: "is used to find all cached pages of a specific site
The operator "allintitle: " allows whole sentences to be identified in web pages.
The operator "inurl: " allows web pages to be located with specific words or sentences in their
The scariest features of the Google engine is its ability to locate "CGI" or "web" scanning
directories containing sample software code or vulnerable files. Using either the "index.of" or
"inurl" operators, and then attaching the desired target directory or file namevulnerable targetswill
be located from the Google data cache.
eg "inurl:admin filetype xls password," produces exactly what you think it would.
For more information enter "Google Hacking" intoGoogle and read the results
-Google Web Toolkit
(GWT) An Ajax development framework for Java programmers.
They write their program front-ends in Java and the GWT compiler converts it to browsercompliant Javascript and HTML
Group of pictures – method of compression used with MPEG
General Protection fault. Windows way of warning that a program
has tried to access a portion of RAM that is protected from unauthorised access. In practice it
means that the program has crashed and the computer needs rebooting. GPFs in user.exe often
mean problems with drivers for sound cards or input output devices like the keyboard or mouse,
while GPFs in gdi.exe often relate to video driver problems. One possible fix is to edit the
config.sys file so that it contains a line 'FILES=100'.
General Packet Radio Service. Allows packet based communication
to take place over a GSM phone network. Often referred to as 2.5G. Data rates quoted as 56Kbps
to 114Kbps though it is usual to achieve speeds of around 40Kbps. Provides a cheaper form of
communication as channels are shared between users and only used during transmission. To
connect to a GPRS network a user needs the (APN) Access Point Name of the network.
Graphics processing unit.
Generic Routing Encapsulation.
-Grid computing
Allows spare processing power of multiple computers on a distributed
network to be applied to a common goal. Method of using many computers around the world for
large projects as in the SETI project.
Used on Windows NT. A predefined collection of access permissions
and rights assigned to a collection of users.
Government Secure Intranet
Global System for Mobile phones. 900MHz or 1800MHz
Graphical User Interface.
One of the major protocols for VoIP. A standard approved by the ITU
in 1996 to promote compatibility in videoconference transmissions over IP networks.
-Half Height
Half height drives are 1.67" tall.
-Half toning.
This process involves laying down larger or smaller dots to create a
more realistic image
Exchange of predetermined signals between two devices establishing
a connection. Part of a communications protocol.
-Hard Drives
Typical rotation speeds of 5400, 7200 and 10000rpm. These
improved drastically with the replacement of the stepper motor with a voice-coil motor. In older
hard disk drives , a stepper motor moved the read/write head along the disk surface in a series of
discrete steps. The new voice-coil motors, however, aren’t limited in their movement by a series of
predetermined increments. Instead, the voicecoil motor spins smoothly, without the slightest
interruption needed to account for the steps. Use of the voice-coil motor also has improved the
average seek time. Average seek time, usually given in milliseconds (ms), measures the amount of
time required to move a hard disk’s read/write head to a particular location. The older stepper
motors accounted for seek times of 120ms. But because the voice-coil motor simply reacts to the
‘voice’ of the magnetic data, the read/write head may move directly to the areas of stored data. The
voice-coil motor allows the read/write head the freedom a computer to move towards any spot on
the disk where data is ‘speaking’. The average seek time is now 8 – 17ms.
Recent jump in storage density has two main causes:
the use of giant magneto-resistive (GMR) read-write heads which increase the sensitivity by
a factor of four. These are being combined with new thin film low noise cobalt alloy storage media
on the platter which provides an ultra smooth surface and allows the GMR head to fly 15nm above
the platter.
spindle speeds have increased to 10,000rpm giving data transfer rates of 325MB/s
Hard Disk Drive Size. Initially restricted to 528MB. This was due to the ATA standard and the
BIOS interrupt (int 13H) that received information about the geometry of the disk, This meant that
disks could have only a maximum of 1024 cylinders. The ATA standard used 16 bits for the
cylinder number, four for the head and eight for the sector. However int 13H used 10 bits for the
cylinder, eight for the head and six for the sector. Since both standards were being used, the
smallest bit depth from each had to be used, meaning a total of 20 bits were used for the geometry.
Despite the fact that Ultra ATA can support up to 137GB and int 13H up to 8.24GB, the
combination of the two meant a 528MB limit.
The solution was LBA (Logical Block Addressing) BIOS translation, which gives each sector on the
disk a unique number and addresses them by this rather than the cylinder, head, sector method.
Overcoming the limitation of the interrupt meant extending the bit depth to 64 bits, which gives a
maximum of 9.4 x 1018 bytes. This left the 137GB limit of 28 bit LBA as the next major barrier and
the possibility of 48-bit LBA would give a limit of 144 x 1015 bytes.
-Hardware Abstraction Layer.
An isolated memory space that programmers can use to write device-independent applications
Hashes are used to make digital signatures of digital data. The
datasets can be of variable length and even the smallest change in the data should result in a
different hash value. MD5 is a common function to produce hashes
-Hayes command set
A set of instructions for controlling basic modem functions such as
dialling, and hanging up, devised by the modem manufacturer Hayes
Host channel adapter, an adapter that connects a server to an
InfiniBand link.
High Definition Compatible Digital. The format is backwards
compatible with standard CD players. It works by using the least significant bit of CD's 16 bits to
encode additional information which results in a 20-bit per channel encoding scheme. Need a
separate HDCD decoder
High level Data Link Control
High Definition Multimedia Interface.
High Definition Digital Television. Two resolutions 1280x720 and
1920x1080. Both are 16:9 widescreen ratios.
High Definition Video. cf DV. Two resolutions 1440x1080 and
1280x720. Usually referred to by their horizontal resolutions and the frame rate. =>
1080/50i and 720/25p or 720/50p where i stands for interlaced fields and p for progressive scan.
Usually employs MPEG2 compression
Half Duplex. Transmission in either direction but not simultaneously.
-Helical scan
Originally used for video recording. The first widely used format for
back up tapes was DDS, the data version of Digital audio Tape. In a helical scan tape drive, the
media is drawn out of the cartridge and passes over a drum that rotates at high speed. The drum
contains both read and write heads and is set at an angle, with data written in offset stripes. This
allows more data to be stored on the tape in a given area. The main disadvantage is the wear of the
tape against the rotating drum
An antivirus technology that looks for indications of virus activity
such as suspicious codes or unanticipated changes in files.
a standard similar to IEEE802.11a.
An European wireless network standard aimed at two different frequency bands - 5.15-5.25GHz and
17.1 - 17.3GHz. Power output is restricted to 1W in the lower band and 100W in the higher. It is
similar to 802.11a in the lower band but less well developed.
High Performance Parallel Interface. See Fibre Channel. It is a
standard for connecting two devices together over short distances. The standard version transfers
32-bits at transfer rates of 800Mbps. Wide HIPPI doubles the transfer rate to 1.6Gbps by
transferring 64-bits in parallel.
Host Intrusion Prevention System
1981 12th August IBM launched the Personal Computer, running DOS. The cheapest was $1565
1982 Compaq Computers introduced the Compaq Portable PC, an IBM clone
1983 Lotus ships the killer PC application - Lotus 1-2-3 spreadsheet, the most complex PC
application of its time.
1985 Intel produces the 80386 microprocessor
1986 Amstrad launches the PC1512, which cost £399
1987 IBM developed OS/2, the first PC operating system that allowed people to use a mouse.
1988 Microsoft becomes the number one software maker.
1989 Tim Berners-Lee and his team at CERN develop the web.
1991 IBM partners with Apple and Motorola after Microsoft falls out with IBM over its big
enterprise OS project, Windows NT
1993 Linus Torvalds develops Linux.
1994 Marc Andressen and Jim Clark release the web browser Netscape
1995 Microsoft launches Windows 95
1997 Compaq moves into high-end computing and buys Tandem for $3bn
1999 Melissa, the world's first macro virus wreaks havoc.
2001 Intel releases the first 64-bit processor, Itanium
2003 AMD releases an entry-level 64-bit processor
2004 IBM sells PC business to Chinese IT supplier Lenovo
A server with an unpublished IP address. Connected to the Internet.
Any access of the server is likely to be from unauthorised activity. Tools running on the honeypot
inspect the incoming TCP/IP connections and can automatically produce signature files that would
allow a firewall to filter out any such packets sent to published servers.
-Hot Plug
Means that a drive can be connected or disconnected whilst there is
power going to it. Mainly used in SCSI based RAID arrays.
High Performance Fortran. A superset of Fortran 90 and often used
on parallel programming clusters
High Speed Circuit Switched Data. Gives 28.8Kbps on a GSM
phone. GPRS the next step forward for higher speed.
High-Speed Downlink Packet Access. Used on 3G phone network.
Theoretical peak data transfer rates up to 14.4Mb/s in downlink and up to 5.8Mb/s in the uplink.
HSDPA is spectrally efficient, so there can be more users per cell.
Also known as 3.5G. It runs over a 5MHz bandwidth on W-CDMA
Hue, Saturation, Luminosity. Hue is a colour defined by a number
between 0 and 360 - as in a colour wheel.
The primary colours are spaced at 120º.
Saturation is like the Contrast on a monitor.
Luminosity is like the Brightness on a monitor.
High Speed Local Area Network
HyperText Mark-up Language. It is effectively a programming
language designed for telling the page what images go where , what links to what etc. It began life
in 1995 as the W3C's answer to incompatibility problems between different suppliers' browsers. It
is based on SGML (Standard Generalised Markup Language) but is much simpler. Now progressed
Hyper Text Transfer Protocol. This is the protocol used by the
Internet to transfer HTML code to your browser for interpretation. Specifies that headers are
separated from the actual content by two line feeds.
Hyper Text Transfer Protocol Secure. This is a secure encrypted
version of HTTP used on e-commerce sites. A closed padlock icon on the browser sometimes
indicates it. Usually uses SSL
The centre of a star topology network or cabling system. When it
receives a signal it refreshes it and strengthens it before passing it on.
-Human Rights Act
Individuals have a right to respect for their private life and
correspondence. Came into effect in the UK on October 2000.
-Hyperlan 2 band
5GHz radio band
A method of presenting information so users can jump around a
document by clicking on a highlighted word or icon.
Intel. Makes more use efficient use of processor resources by running
more of them in parallel. Hyper Threading splits a Pentium 4 or Xeon processor into two logical
CPUs, so that if two sets of instructions use different registers they can be processed at the same
time. However, the two threads need to be complementary - so that they don't execute the same
instruction at the same time.
runs at 51.2Gbps. Links the IGP (Integrated Graphics Processor and
the MCP (Media Communications Processor). It is a royalty free and open industry standard for the
point to point link for ICs. The technology provides a universal connection, designed to reduce the
number of buses within a system and provide a high performance link for embedded applications. It
also aims to enable highly scalable multiprocessing systems. The interface delivers 16Gbps bus
Intel Application Accelerator - Improves IDE Disk Drive access for
Intel chip sets.
Integrated Access Devices
Internet Assigned Numbers Authority.
The following IP addresses are reserved for private local networks. - - -
Internet Authentication Service. W2k VPN
International Financial Reporting Standards. To replace GAAP
-IC sizes
Athalon and Pentium III, the components are 0.18m and the
pathways joining the components are only about 100 molecules wide.
The Internet Corporation for Assigned Names and Numbers.
Internet Connection Firewall
Internet Control Message Protocol. Runs in the Network layer. It
reports unexpected events and is encapsulated as an IP packet. The allowed messages include:
Destination unreachable
Warns that the packet could not be delivered.
Echo request
Asks a machine if it is alive.
Echo reply
Responds to an echo request.
Parameter problem
A field in the header was invalid.
Source quench
Tells a fast transmitter to back off as it is flooding the receiver.
Timestamp request
Same as echo request but asks for a timestamp as well.
Timestamp respond
Reply to timestamp request.
A practical use of ICMP is PING, which sends an echo request to make sure that a remote computer
is up and running.
Intelligent Document Architecture
Integrated Drive Electronics. The most popular type of hard drive
system. The controller electronics are included inside the device. The electronic intelligence for
operating the disk is inside the hard disk itself. Limitations; disks smaller than 528MB, only two
hard disks in one computer. Max transfer rate about 4MB/s.
Integrated Development Environment. Used by programmers for
enhancing productivity when programming.
Intrusion Detection System
Interactive Digital Television
See Internet Explorer
Institute of Electrical and Electronic Engineers. The US based society
that uses its own standards and is a member of ANSI and ISO.
-IEEE 1394
A peer to peer communications system. Allows 63 peripherals on the
same connection. The standard allows for up to 1023 busses to be bridged together.
1394b specification provides connection speeds of 800Mb/s
An Ieee standard for providing quality of service within a LAN
The initial draft of the WLan standard. It provides 1 or 2Mbps
transmission using the 2.4GHz band.
Wireless standard - up to 54Mbps using the 5GHz band. Ratified
after 802.11b. Intended to have a range of over 200ft in an office environment.
-IEEE 802.11b
Wireless standard - up to 11Mbps over a radius of 100m using the
2.4GHz band. First ratified in 1999. Uses 24 bytes of pre-amble in the physical layer. PLCP Physical Layer Convergence Protocol. Also known as WiFi. 2.4GHz to 2.4835GHz. This
frequency band is also used by Bluetooth, microwave ovens, ISM equipment.
13 different channels (numbered 1 to 13). Cards can only listen to one channel at a time.
83MHz wide - divided into 11 x 22MHz wide channels all of which overlap with each other apart
from channels 1, 6 and 11.
-IEEE 802.11e
Defines quality of service for WLANs, to support voice over IP, for
-IEEE 802.11g
Successor to 802.11b. Achieved by the use of OFDM. In theory
54Mbps possible at 2.4GHz.
-IEEE 802.11h
This is the extension of 802.11a which introduces the power control
and frequency features required by European legislation. The frequency range 5.25 - 5.35GHz is
used by a number of military and satellite radar networks. So in Europe can only access the first
four frequencies within Band A (5.150 - 5.350GHz). This standard requires equipment to have
TPC (Transmit Power Control), which limits the transmit power to the absolute minimum and DFS
(Dynamic Frequency Selection), which allows wireless equipment to shift frequency if a radar
signal is detected. MaxEIRP is 60mW for equipment without TCP and 120mW with TCP.
-IEEE 802.11i
Wireless security standard of which WPA is a subset. A secure
replacement for WEP
-IEEE 802.11j
The Japanese equivalent of 802.11h
-IEEE 802.11n
A proposed spec to double the speed of 802.11a/g WLAN.
Equipment expected in 2006. Speeds of 150Mb/s to 350Mb/s - rising to 600Mb/s
-IEEE 802.11n-MIMO
Multiple Input Multiple Output. A number of aerials transmit many
unique data streams in the same frequency channel
-IEEE 802.15
A standard for personal area networks, based on Bluetooth
-IEEE 802.16
Specification for fixed-wireless broadband.
-IEEE 802.16a
Allows the use of the 2GHz to 11GHz range for WLANs. Also called
WiMax, can transfer up to 70Mb/s over as much as 30 miles
-IEEE 802.1x
Authentication scheme based on EAP (Extensible Authentication
-IEEE 802.20
Proposal for 1Mb/s wireless metropolitan area networks
-IEEE 802.3
A physical layer standard that uses the CSMA/CD access method on a
bus topology LAN. Defines 10Mb/s Ethernet.
-IEEE 802.3u
Standard which defines 100Base-T or fast Ethernet. Finalised 1997
High speed applications bus. Also known as Firewire.
-IEEE P802.3ae
10 Gb/s Ethernet standard. Also known as 10GE
Interactive Electronic Mail Standard Identification. Universal e-mail
standard so that it can be used cross platform
Internet Engineering Task Force. Working to improve the capacity,
performance of SANs and the internet in general. Defines standard internet operating protocols
such as TCP/IP
Internet Fibre Channel Protocol A SAN interconnect protocol.
Floating pop-up frames.
Integrated Graphics Processor. Integrated Graphics Port.
Microsoft Internet Information Server - web server for Windows.
Intermediate Language.
Information Lifecycle Management
Instant Messaging.
IP Multimedia Subsystems. Developed by 3GPP to provide the
telecom industry with a modular, standards-based IP/SIP service delivery infrastructure.
Internet Message Access Protocol. A method of sending email across
the Internet. Originally developed in 1986 at Stanford University - similar in operation to POP3 but
offers better interaction between e-mail clients and servers.
The Windows Communication subsystem in Windows Vista.
the next generation of I/O architecture and is set to replace PCI. It
offers throughput of up to 2.5Gbps and supports 64000 addressable devices. Uses a serial bus in a
similar way to a network.
-Inkjet printer
Squirts minute drops of ink from tiny nozzels directly onto the paper.
Based upon thermal print heads, though the Epson stylus range use a piezoelectric mechanism to
squirt the ink drops. the nozzels are around 1/500th of an inch. The ink is heated to around 1000ºC
in the nozzle for 3 millionths of a second. The intense heat causes the ink to boil and form a bubble
(hence the name BubbleJet used by Canon.). As the bubble bursts, a tiny quantity of ink is forced
through the nozzle and onto the paper. Tend to be slow and expensive to run.
Deleting visits.
Navigator's Cache folder is inside the Navigator folder.
Internet Explorer's Cache folder is inside the Windows Temporary Internet Files folder
Navigator's cookie folder is called cookies.txt. Find using Windows find.
Internet Explorer keeps its cookies in a folder called cookies inside the windows folder.
History files. Netscape Navigator in the netscape.hst file.
Internet Explorer look in the Windows\History folder.
Registry: Use the Registry Editor window, select Edit, Find and then enter URL History. Select
and delete the URLs but not the default listing
Navigator users should also select and delete the URLs they find in
hkey_local_machine/software/netscape/netscapenavigator, opening the version number folder if
Internet explorer users will find additional URLs in
Deleting all traces of Web activity.
Run the batch file after closing the browser.
For Netscape Navigator:
echo y>c:\windows\tempor~1\y.txt
del c:\progra~1\netscape\naviga~1\cache\*.*<c:\windows\tempor~1\y.txt
del c:\progra~1\netscape\naviga~1\cookies.txt
del c:\progra~1\netscape\naviga~1\netscape.hst
del c\windows\cookies\*.*<c:\windows\tempor~1\y.txt
del c:\windows\history\*.*<c:\windows\tempor~1\y.txt
del c:\windows\tempor~1\*.*<c:\windows\tempor~1\y.txt
For Internet Explorer
echo y>c:\windows\tempor~1\y.txt
del c:\windows\cookies\*.*<c:\windows\tempor~1\y.txt
del c:\windows\history\*.*<c:\windows\tempor~1\y.txt
del c:\windows\tempor~1\*.*<c:\windows\tempor~1\y.txt
Or use NSClean Privacy Software from for Netscape Navigator or
IEClean for Internet Explorer from the same place.
Address books with file suffix *.pab or *.wab
Based on 10Gb/s Ethernet. It is a consortium led by 207 universities
working in partnership with industry and government to develop and deploy advanced network
applications and technologies. One of the projects to come out of Internet2 is Abilene, part of the
Internet2 backbone network and a system that enables US-wide testing of applications such as
uncompressed high-definition TV-quality video; remote control of scientific instruments such as
mountaintop telescopes and electron microscopes; collaboration using immersive virtual reality; and
grid computing.
-Internet Country codes
Czech Republic
New Zealand
Saudia Arabia
United Kingdom
United States
South Africa
-Internet Explorer
Kiosk mode iexplore -k Allows internet explorer to run full
IE6 - need to install Quicktime -
IE6 - need to install Java Virtual Machine -
IE6 - Disable Error reporting to MS. On non XP machines
HKEY_LOCAL_MACHINE\Software\Microsoft\Internet Explorer\Main. Create DWORD value
called IEWATSONENABLED and set value to 0.
IE6 - printing. Text scaling with CTRL and mouse scroll wheel.
Headers and footers - use printer control codes
Window title
URL in full
Date (short)
Date (full)
Time (24hr)
Current page number &p
Total page count
Right align
Centre align
Security settings. Adding to Trusted and Restricted sites
* eg *
Internet Network Information Centre.
Translates a high level language to machine code one statement at a
time and executes it before translating the next statement.
-Interval Arithmetic
Notes the boundary values of uncertain parameters and removes the
levels of inaccuracy
information etc
A private internal network, based on TCP/IP, for providing
-Invalid page Fault
Caused when a page of data or program code in the swap file cannot
be loaded into the main memory.
Internet Protocol. Usually a set of four numbers eg
Everything that is connected to the Internet has its own unique number. LANs may have just one IP
address to connect to the outside world. ISPs do not have enough IP addresses to go round and so
will allocate dynamic IP addresses, which change each time you log on.
IP protocol corresponds to the network layer in the seven-layer OSI model. The IP datagram
consists of a header that contains addressing and general options and a data part. The header has a
20 byte fixed part and a variable length options part. See diagram below.
IP header
32 bits
type of service
time to live
total length
fragment offset
header checksum
source address
destination address
options (0 or more words)
Version of IP being used IP v4 or IP v6
Contains the length of the header. The minimum value is 5 when there are no
options and a max value of 15, which restricts the options field to 40 bytes
and the header to 60 bytes.
Type of service
Defines the level of service that a packet gets, eg streaming video needs fast
delivery and file transfer needs reliability. This field contains a three bit
precedence field, three flags (D, T and R) and two unused bits. precedence
takes a value from 0 to 7 which specifies the priority of the datagram. The
flags are used to emphasise what the datagram finds important, delay,
throughput and reliability. In practice most routers ignore this field.
Total length
This 16 bit field specifies exactly how long the datagram is including the
header. The maximum length of the packet is therefore 65,535 bytes.
Tells the receiving computer which datagtram a fragment belongs to. All
fragments in a datagram have the same identification value.
The next bit is unused.
A one bit field that means 'don't fragment'. It tells routers that the receiving
computer cannot reassemble fragments. However all machines are required
to accept fragments of 576 bytes or less.
A one bit field that means 'more fragments' and is used to instruct the
receiving machine that more fragments are on the way. All fragments, except
the last, are marked with this field. If the field has no entry, then it means
that this fragment is the last.
Fragment offset
A 13 bit field defines exactly where in the datagram the fragment belongs. It
helps the destination machine reassemble the datagram in the correct order.
All fragments, except the last, have to be a multiple of eight bytes long. The
13 bits give a maximum of 8192 fragments, which gives a maximum
datagram length of 65536 bytes (8192 x 8), which is one byte more than the
total length field.
Time to live (TTL) An eight bit field that determines the time in seconds that a packet can stay
on the network. This gives a maximum of 255 seconds. Prevents a datagram
bouncing around forever. In practice the TTL field is decreased by one every
time it hakes a hop. When the TTL hits 0, the datagram is removed from the
network and a warning sent to the source host.
Defines which protocol to use for the transport process. Most common are
TCP and UDP.
Header Checksum
This field carries a checksum for the header alone. Used to ensure that it
does not get corrupted. It has to be updated at each hop as some fields, e.g.
TTL, will change each time.
Source Address
32 bit field giving the origin of the datagram.
Destination address 32 bit field giving the destination of the datagram.
Currently only five options are defined, but not all routers support them.
How secret is the datagram?
Strict source routing Defines the route to take.
Loose source routing Lists routers that can't be missed
Record route
Traces the route by making routers append their IP addresses.
Each router appends its address and timestamp.
Typically the 40 byte length of this field is not long enough for the record
route and timestamp. The options length limit was set in the early days of
Arpnet when no datagram ever passed through more than nine hops.
-IP Addresses
A 32 bit binary number often quoted as 4 eight bit numbers. This
gives each quarter of the address a maximum value of 255. The full address is actually a
combination of two addresses: host and network. The network address is used by routers to get a
datagram to the destination network e.g. Once the datagram reaches the network, the
network address is ignored and the datagram routed to the correct host.
Networks are classed by A, B and C domains. There are also class D and E domains but they are for
multicast use.
IP address ranges
32 bits
host address range to
network to
host to
The diagram above shows how the header on the IP address differentiates each class of network and
the range of IP addresses available to the host.
Each class defines the number of bits to use for the network and host address respectively. A larger
network address reduces the number of hosts on the network. The table below shows how many
networks can exist in each class and the number of hosts that each network can hold.
Number of networks
seven bit address: 126
14 bit address: 16384
21 bit address: 2,097,152
Number of hosts per network
24 bit address: 16,777,216
16 bit address: 65536
eight bit address: 256
In addition to this there are several reserved addresses. is used by hosts while they are
booting, but not used after that. IP addresses that have a network address of 0 refer to the current
network. This allows hosts to transmit to local machines without knowing the network they are on.
However they need to know the class of the network so that they can insert the correct number of 0s.
Broadcasts are handled by filling the address with 1s, which sends packets to all machines on the
local network. Broadcasts can be sent to remote sites by filling out a proper network address, but
putting all 1s as the host address.
All addresses in the 127.X.X.X space are reserved for loop back testing. Packets sent to that
address are not sent out but are processed locally. This is typically used for debugging and usually
with the address
192.168.0.x This range of IPs is allocated for use by private networks that are not directly
accessible via the internet. Use subnetmask of
Intelligent Parallel Interface. See Fibre Channel. A high bandwidth
interface between a computer and a storage device. Operates with transfer speeds of 25MBps and
supports RAID.
Internet Print Protocols.
Intrusion Prevention System. Two types - Host IPS (HIPS) and
Network IPS (NIPS)
Internet Protocol Security
Gives a 32 bit number
Gives a 128 bit number compared to the 32 bit number of IPv4 giving
approximately 340 billion, billion, billion, billion, billion, billion, billion unique addresses.
Numbers written in hex and separated by colons not dots.
ABCD:0000:0000:0000:00FE:22DC:FFDE:CAD2 Leading zeros can be omitted.
ABCD:0:0:0:FE:22DC:FFDE:CAD2 Strings of consecutive zeros can be replaced by two colons
IP-based Virtual Private Network. Either delivered over a private IPbased network or the public internet
Internet Packet Exchange / Sequence Packed protocol. Compatible
with both Windows and Novell Netware. Not suitable for the Internet or even wide area networking
in most cases, IPX is a connectionless protocol best applied to 'bursty' LANs where data traffic
flows in fits and starts rather than continuous streams. The other half of the partnership - SPX- is
connection orientated. It is used to establish permanent or long term connections between specific
network nodes which copes with a large and regular amount of traffic.
Internet Relay Chat
Information Rights Management
Interrupt ReQuest. A signal that interrupts the processor to gain its
attention. PCs support up to 15 separate IRQs.
Every PC has 16 IRQ lines.
PCI bus allows more than one device use a single IRQ.
MSD in Win3.1 shows IRQs.
Win95; right click My Computer, choose Properties, click the Device Manager tab and double click
the Computer Icon for a complete list.
Note: IRQ2 and IRQ9 are actually one IRQ.
IRQ5 is the most popular assignment for expansion cards, eg SoundBlaster.
Every PCI card shares the single IRQ that the system assigns to the PCI bus, often IRQ11.
Industry Standard Architecture. The original PC setup which allows
extras to be added to a system by inserting plug in adapter cards into slots on a mother board. These
are 16 bit slots and are usually coloured black on the motherboard.
Internet SCSI. The oldest of the SAN interconnect protocols.
SCSI commands are sent inside IP packets. The receiving station takes the commands out of the
packet and passes it to the SCSI controller, which makes the request to the storage. The result is
packaged back up in an IP packet and returned to the originator.
Integrated Services Digital Network. See Digital Telephony.
Enables the transmission of digitised signals over existing telephone network.
A basic rate ISDN line has three channels - two 64Kbits/s B channels (Bearer channels) and a
16Kbps D Delta) data channel that is used for signalling third low capacity of about 90 to
Primary rate ISDN consists of multiple B channels and one 64Kbps D channel. Two standards European and American. European standard is 30B + D to give the 2.048Mbps of an E1 line. In the
US it is 24B + D to give the 1.544Mbps of a T-1 line. Signalling is carried out on the D channel.
Data sent over the B channels is sent without framing information and with no error detection or
correction. It is left to the end devices to deal with this.
Information Society Initiative. A DTI-led scheme, which represents
the government's broad brush IT adoption program that aims to promote the use of computers and
IT in general in all areas of modern society.
-ISM band
Industrial, Scientific and Medical band - 2.45GHz
International Standards Organisation
Standard for defective pixels in flat panel displays. Drafted in 1999
and finalised in 2001. It covers all ergonomic aspects of TFT monitors including uniformity of
colours, contrast and brightness as well as reflectivity, flicker and pixel defects. The standard
defines four types of defect. The first is where a whole pixel is continuously lit. This gives a white
spot on a black screen. The second type is the opposite of the first - giving a black pixel on a white
screen. The third is where there is a subpixel failure - resulting in a coloured pixel on a bright or
dark screen, eg a blue dot. The fourth type of defect is referred to a fault cluster and is the number
of types one, two and three defects in a five by five pixel area. There are four classes to the standard
and the pixel faults per million pixels are shown in the table below.
Type 1 Type 2 Type 3 Type 4 with Type 1 or
Type 4 with Type 3
Type 2 faults
Class IV allows as many as 500 defective pixels, class II between 1 and 5 and class I no defective
ISO 27001
New formal standard against which organisations can seek
independent certification of their Information Security Management Systems. Replaces BS7799
Part 2.
Internet Service Provider. A company that hosts machines constantly
connected to the Internet. You dial into one of their modems and connect to the network giving
access to the Internet
Interrupt Service Routine.
IT Infrastructure Library - a series of documents used to aid the
implementation of a framework for IT service management. The framework is customisable and
defines how service management is applied within an organisation.
Intelligent Tag Reader
International Telegraphic Union - Telecommunications Standards
Sector. Replacement organisation for CCITT
Interexchange carrier, or a service provider specialising in long
distance transport services across multiple local exchanges
Continuously sending random data; normally used to describe the
action of a station that locks up the network with its incessant transmissions. Often caused by a
damaged NIC.
Can also be used in connection with Ethernet networks. The 802.3 standard defines a minimum and
maximum packet size. A jabber is a packet that is larger than the 1518 byte defined limit.
The private network for the academic community in the UK. It is
managed by UKERNA for the Joint Information Systems Committee (JISC) of the Higher
Education Funding Councils for England, Scotland and Wales.
JANET Computer Emergency Response Team.
An object-orientated programming language that enables software
developers to create interactive elements that work across operating systems. This makes Java an
ideal language for Web programmers.
Developed by Sun Microsystems in 1995. Intended to be hardware non specific
An evolution of C++. Object orientated. Java is interpreted and the interpreter is called the Java
Virtual Machine or JVM. A JVM has been developed for several different platforms. Java
compiles to an intermediate format called byte code that should run on any JVM. Java can be
embedded in a web page.
A scripting language, similar to Java, which allows Web programmers
to create dynamic content, such as interactive games or search engines on their Web sites. Produced
in 1995 by Netscape for use with its Navigator browser. Its name was changed from Livewire to
Javascript because its syntax resembled Java.
Java API XML an open standard proposal for interfacing with event
driven XML processors.
JISC Committee on Networking. A sub-committee of JISC which is
responsible for the UK networking programme for higher education and research.
JANET Connection Point.
JANET Customer Service
JANET Connection and Upgrade and Request form
Java 2 Enterprise Edition
JANET Information Systems Committee
Just In Time. Intermediate language run time compiler
JANET Operations Desk. Based at ULCC, and provides a single
point of contact for computing service staff to report faults on any of the JANET Operational
Joint Photo Experts Group. Supports both 16 and 32 bit images so
ideal for photographs. Lossy compression. Can use 16.7 million colours at a much higher
compression than GIF.
A development environment for Java-based server software.
Java server Pages. A scripting language based on Java for developing
dynamic web pages and sites. Often used on Solaris and Linux platforms
Java Virtual Machine. Interpreter for Java.
Worm virus. install security patch. Attaches itself to
all outgoing messages; alters the registry; closes the PC at 5pm on the first day of every month.
Kilobits per second
A file transfer protocol. When it breaks a file into packets, each
packet is bracketed by control data. The receiving computer checks each packet's control data as it
arrives and acknowledges to the sending computer.
The device drivers that enable hardware to communicate with
software applications. The kernel sits between the hardware (such as hard drives or video cards etc)
and software, and also provides a library of standard routines, such as for opening a file or changing
user ID.
-Keyboard plugs.
Keyboard Data
Keyboard Clock
Keyboard Reset
Open Source web development program. Linux, Apache, MySQL
and Perl, Python or PHP
Local Area Network. A network of computers in a relatively small
area. Each computer (or node) has its own operating system, but can access files or use devices
such as printers or modems across the network.
To link two computers enable NetBEUI, IPX/SPX and TCPIP. Primary network log-on set for
Client for Microsoft Windows. Give each computer a unique name and make sure that they are
both in the same workgroup.
-LAN Manager
A network operating system developed by Microsoft and 3Com for
use with the OS/2 operating system.
-Laser printers
Link Access Protocol and MNP 1-4
Based on the same principle as the photocopier. First laser
printers made by Xerox. The digital signals turn on and off a beam of light which is generated by a
laser. This hits a spinning mirror which deflects the beam onto a photosensitive drum. The point at
which the light hits the drum, a positive electric charge is produced and the toner attaches
electrostatically to these areas. The paper then picks up the toner off the drum and passes through a
heater or fuser which fixes the image to the paper. Instead of using a laser to generate the light,
some printers have a row of tiny LEDs.
LED/LASER printers The printers processor controls a light source that is projected onto a light
sensitive drum. This creates a positive charge on the drum's surface at the points where the light
hits, creating a pattern that will represent the output image. The drum rotates past the toner
cartridge, upon which the negatively charged toner particles are attracted to the positively charged
portions of the drum. These are transferred onto the negatively charged paper, which passes next to
the drum after it has passed the toner cartridge. Finally the toner particles and paper are heated in
the fuser unit to bond the particles to the paper so creating the image.
It is the light source that differs in LED and laser printers. In a laser printer an arrangement of
lenses and mirrors reflect and refract the beam across the surface of the drum. Since the drum is
rotating, precise timing is needed to retain a straight horizontal beam path across the drum. Parallax
correction is also used to keep the beam focuses at the edges of the drum.
By contrast, an LED array is a relatively compact and sturdy arrangement that shines light through
focusing lenses directly across the width of a rotating drum. This eliminates parallax and timing
errors. As there are no moving parts, LED technology is more reliable than laser. Also a LED array
can enable faster print speeds since multiple light sources shine on the entire width of the drum
allowing it to rotate faster.
Because of its compactness, LED technology comes into its own in colour printers. It can enable
single-pass printing by employing four separate print head units each incorporating a LED array and
a photoconductive drum, one for each toner, cyan, yellow, magenta and black. As a result LED
colour printers are nearly as fast as monochrome printers. Colour laser printers have to pass the
paper through the electrophotographic process four times, one for each of the four colours.
Disadvantages of LED printers: the number of LEDs fixes the horizontal resolution of the printer.
So resolution enhancement techniques can never be as effective as those of laser printers since the
laser beam intensity can be varied. The quality of LED arrays also degrades with time as the
intensity of individual LEDs weaken at different rates, leading to streaking and non-uniform
printing across the page. This also is the reason why LED printers are inferior for producing
To print in colour, the paper either has to make four passes under the photosensitive drum, one for
each colour or there have to be four different toner hoppers around the same drum. To ensure that
only the cyan toner goes to the cyan bits etc is usually done with different charging voltages.
Charging corona
Photosensitive drum
Toner reservoirs
Cleaning blade
Paper path
Transfer belt
This is the time it takes a hard drive to access data, not just find the
data as in seeking and is based on the drive rotating half a revolution. The lower the figure the
The time in ns or clock cycles between a request to read memory and the data being output.
-Layer model
The OSI Open Systems Interconnection model
Large Block Addressing. Needed to work with drives larger than
Logical Block Addressing. - abandons the usual cylinder/head/sector
divisions of a hard disk and substitutes a single address which is used to number each sector of the
hard disk consecutively.
An expensive technology used in data projectors. Also known as DILA technology. Combines the use of LCD and DLP technologies to give a good image. Very
expensive currently. LCOS is a reflective technology that constructs the image on a mirror substrate
covering the chip. Rather that using thousands of individual mirrors to construct the image, the
LCOS mirror substrate is coated with liquid crystals that can open and close to modulate the light in
a similar fashion to LCD technologies. These projectors actually contain three LCOS ICs, on eof
reach of the main colours. This means that it does not need a rotating spinning colour wheel.
Very high resolution compared to the other projector technologies.
Lightweight Directory Access Protocol. Network policy schemes
from Microsoft, Novell etc. A lightweight replacement for the old X.500 mechanism that enables
applications to access a directory service. It is used in identity verification and single sign-on
applications. It defines the method by which directory data will be accessed; not how, or in what
kind of database that information will be stored and manipulated. It is cross-platform and standards
based, so it is not limited by hardware, operating system or database, and provides a basis for
integration of directories within and between organisations.
LDap-aware client applications use standard protocols and filters to request LDap servers to look up
indexed data. LDap client applications and servers from different suppliers should not need to be
customised to work with one another. In fact, beyond the use of the protocols and query commands,
LDap does not specify how either client or server application needs to work.
It originated at the University of Michigan in the early 1990s, to provide most of the functionality of
X.500/X.519 without the need to implement a full OSI protocol network stack.
LDap enables data kept in different directories managed by multiple applications to be unified and
managed centrally.
Laser Guided Magnetic Recording. Used by Super DLT, which
employs optical and magnetic methods to greatly increase the data storage capacity of cartridges.
-Linear tape drives
Or Longitudinal Serpentine technology. The data tracks run in
parallel over the length of the tape and data is written sequentially until the end of the tape is
reached. Then the read/write head simply moves up one track, and writes data in reverse until it
reaches the beginning of the tape again. Because of the parallel layout, extra read/write elements
can be put into the tape head to increase transfer rates and boost capacity. The technology tends to
give better reliability, capacity and transfer rates.
-Line driver
A DCE device that amplifies a data signal for transmission over cable
for distances beyond the RS232/V.24 limit of 15.2m
Or Linker loader is software which links two or more separately
produced object code files (compiled programs) into a single program. The linker is also used to
link object code programs with the library routines called within the programs. Library routines are
simply additional object code programs
-Link Layer
Layer 2 of the OSI reference model. Also known as the Data Link
Created by Linus Torvalds. GNU recursive acronym for GNU's Not
Unix. Linux is strictly the kernel of the OS. Little penguin called Tux. Linus Torvalds was a
student at the university of Helsinki - had enrolled on a Unix course in the autumn of 1990. Being
unable to afford Unix, but with access to the source code of a Unix-like OS called Minix, he wrote
the device drivers for his own PC and gradually built up the kernel in 1991. It was released onto the
web in 1991 and the first stand alone version was launched in 1992.
The National Access Point for the Internet for the UK. Located in
Telephone house in London's Dockland. Data rates of 3Tbps.
Logical Link Control. A protocol developed by the IEEE 802
committee for data link level transmission control. The upper sublayer of the IEEE Layer 2 OSI
protocol that complements the MAC protocol. IEEE 802.2. Includes end-system addressing and
error checking
Local Loop Unbundling. Leasing out local copper cables to other
Telecom providers
Learning Management Systems. Tracks progress of students through
lessons and provides reports to monitor the learners performance.
The Windows start up screen file/image. Needs to be 256 colours and
320x400 pixels.
-Long file names
Can be up to 255 characters in length. Can be backed up and restored
in DOS using lfnbk.exe. Instructions for using lfnbk.exe are found in Windows95 Resource Kit
help file Win95rk.hlp, which is in the Admin\Reskit\Helpfile folder of the CD.
Diagnostic test in which the transmitted signal is returned to the
sending device after passing through all or part of the data communications link or network.
permits the comparison of the returned signal with the transmitted signal.
-Loose Tube Fibre
Out door optical fibre cable. Filled with gel and other water repellent
outer jacket
aramid yarn loose tube
optical fibres
strength member
Low Smoke Zero Halogen cables have a special jacket, that when set
alight does not pollute the atmosphere with harmful and toxic gases.
-Love Bug
e-mail virus. Some of its effects. resets IE startup page installs
files love-letter-for-you.* Funny Love.* MSKernel32.vbs Winfat32.exe Win-bugsfix.exe It
also steals your internet access passwords and e-mails them to an address in the Phillippines
-Low Profile
The height of the drive is 1".
Linux Professional Institute Certification
Linear Tape Open. Back-up tape format. LTO3 gives up to 800GB
compressed and up to 490GB/hr. Costs around £4k. The system is backed by IBM, HP and
Certance. LTO Ultrium: Generation 4 offers a transfer rate up to 240MB/s based on 2:1
compression and a capacity of 1.6TB. Generation 5 will reach 3.2TB at 350MB/s and generation 6
will reach 6.4TB at 540MB/s
-LU 6.2
A set of protocols that provides peer to peer communication between
A lossless method of picture compression - used in both GIF and TIF
files. It works by employing an algorithm to find repeated pixel combinations and builds a table to
represent them. The result is typically 30% smaller than the original. LZW was subject to a patent
held by Unisys, but they do not intend renewing this when it expires.
-MAC address
Medium Access Control address, often called the physical address.
-Macro virus
The most common kind of virus and account for about 80% of
all infections. Usually applied to Microsoft Word and Excel documents.
Internet worm virus. Can erase all data from the hard disk. Deletes
information in CMOS memory and flash the BIOS. Sent as a .exe e-mail attachment. The e-mail
subject header and body text are randomly generated from documents on the hard disk of the
affected computer. You should query the unexpected receipt of an e-mail about a random topic.
Generic name for all malicious computer code
Metropolitan Area Networks
-Manchester Encoding
Digital encoding technique specified for the IEEE 802.3 Ethernet
baseband network standard. Each bit period is divided into complementary halves; a negative-topositive (voltage ) transition in the middle of the bit period designates a "1", while the a positive-tonegative transition represents a "0". The encoding technique also enables the receiving device to
recover the transmitted clock from the incoming data stream.
Message Application Program Interface
Mail Abuse Prevention System - their web site provides advice on
preventing relaying by mail servers.
Presence of signal. In telegraphy, a mark represents the closed
condition or current flowing - equivalent to a "1".
Media Access Unit. A single device that combines the function of a
transmitter and receiver. Also known as Multistation Access Unit. Used on a Token Ring LAN
Master Boot Record is located at the very beginning of the hard drive
(side 0, track 0, sector 1). The systems ROM BIOS bootstrap loads and executes the bootstrap
loader contained in the MBR. This lets the system know which partition is the startup partition.
Mobile Broadband Wireless Access. Ieee P802.20. Operates in the
3.5GHz band and can provide 1Mb/s at up to 15km. Can link moving client devices travelling at up
to 250km/hr
Memory Channel 2. Used for the fast transfer of data between
Microchannel Architecture. A 32-bit slot expansion card introduced
by IBM. Ran at 8MHz.
Media Centre Edition - version of Windows XP with the Media Centre
Media Centre Extender
Microsoft Control Interface - used with video cards.
Media Communications Processor
Microsoft Certified Professional
Microsoft Certified Software Engineer.
Mail Delivery Agent. Delivers e-mails. The most common MDA is
remote POP3.
Multiple Document Interface. Used by Office 97. See SDI
Metropolitan Ethernet Forum - alternative to ADSL and DSL.
Micro-Electromechanical Systems.
SDRAM, Synchronous DRAM was the successor to EDO and was
near universal until recently. The main specification for SDRAM is its access time, in ns, and is
usually the last number printed on the chips themselves. Early memory was 12ns and quickly
improved to 10ns. 100MHz CPUs led to yet faster memory, usually 8ns. This led to the definition
of the PC100 standard, with PC66 being used to refer to the older 10/12ns memory. PC133 led to
7.5ns and PC150 and PC166 is appearing. The most common form factor is the 168-pin DIMM.
Memory supported by the various chip sets:
Intel 440BX
Pentium II/III, up to 1GB of PC133
Intel 810x
Pentium III, up to 512MB PC133
Intel 815x
Pentium III, up to 512MB PC133
VIA Pro133A
Pentium III, up to 2GB PC133
VIA KT133x
Athalon, up to 2GB PC133
ServerWorks LE
High end Pentium III/XEON, up to 4GB PC133
ServerWorks HE
High end XEON, up to 16GB PC133
SiS 630
Pentium III, up to 1.5GB PC133.
RDRAM Rambus memory. Rambus Corporation. Speeds known as PC600, PC700 and PC800
and the form factor is the 184-pin RIMM. Intel is the only mainstream manufacturer to design for
Intel 820x
Pentium III, up to 1GB PC800
Intel 840x
Pentium III, up to 4GB PC800 interleaved
Intel 850x
Pentium 4, up to 2GB PC800 interleaved
DDR SDRAM This is the newest type of memory. Uses a lower voltage than regular SDRAM and
exploits the PC clock timing signal to double the data rate transferred in a single clock cycle.
Specified as PC1600 or PC2100 - referring to the peak data transfer rate in MB/s and the form
factor is a 184-pin DIMM. Only three manufacturers support this chip set:
Athalon up to 4GB
VIA pro266
Athalon and Pentium III variants up to 4GB
ALi MAGiK/ALADDiN(4) Athalon and Pentium III variants up to3GB.
In theory PC133 runs half a second faster than PC100. In practice compatibility issues with
memory can lead to difficulties.
Interleaving is awell established practice of increasing memory performance by
addressingmultiplememory segments in parallel (like disk striping). For this modules have to be
installed in pairs. Only works on boards that have even numbers of RAM slots.
VIA and ALi DDR chipsets have the capability of addressing both SDRAM and DDR SDRAM but
only ALi boards have both sockets.
Major on Third - Major memory manufacturer mounted on a third party board.
Major on Major - Major memory manufacturer mounted on a their own board.
Registered memory - Used for high end/mission critical systems, where the data must arrive as
intended. Called Registered because it contains a register that delays all data transfer to the memory
module by one clock cycle to make sure that everything is there. Tends to be more expensive and
slower than non-registered memory.
Buffered memory - designed to handle large electrical loads in systems that have a massive amount
of memory installed.
Expanded memory - divides memory beyond 1MB into small chunks called banks which can be
used by DOS.
Extended memory (XMS) - any memory beyond the 1MB limit. Can address the whole of memory
without swapping banks in and out.
Upper memory area - between 640Kb and 1024Kb used to hold device drivers instead of using
conventional memory.
Old 486 machines use 30 pin SIMMs (about 3 inches long). Usually installed in banks of four
Pentiums use 72 pin SIMMs (about 4 inches long). Usually installed singly in 486s and in pairs in
DRAM dynamic random access memory.
EDO RAM extended data output RAM. Provides a 10 to 15% speed improvement.
SDRAM Synchronous DRAM. Uses the clock to harmonise data input and output on a memory
module. The clock is in complete synchronisation with the cpu, thus reducing any lag between cpu
requests and memory activity.
RDRAM Rambus DRAM. Meant to be very fast.
Cache memory. To get round the performance lag in DRAM, special high speed memory can hold
data and applications and allows the cpu to have faster accesss than if they were stored in main
memory. Cache memory works in conjunction with the main memory and the cpu using a separate
Level 1 cache is stored within the cpu.
Level 2 cache is stored on the mother board.
-Memory Test
October 2002 PCA
An any to any network in which a node is connected to virtually any
other node in a collection of cross-connect links, implemented using OXCs. Can allow very
efficient routing, but can be expensive to implement.
Media Gateway Control Protocol (MGCP) - also known as H.248 and
is one proposed standard for replacing the older H.323 for the conversion of audio signals carried
over the PSTN to packets for data networks. Developed by Telcordia and Level 3 Communications
and has been accepted by the IETF as Megaco and as H.248 by the Telecommunication
Standardisation Sector of the ITU. The older H.232 was previously okay for Lans but it did not
scale to larger networks. The growth of VoIP has seen a need for a better protocol. MGCP is
designed to make IP telephony devices cheaper because it eliminates the need for them being
complex, processor intensive devices. It does this by using a media gateway controller to setup,
maintain and terminate calls between endpoints. Part of this puzzle is to make sure that all
endpoints involved in a communication are working at the same rate. MGCP's controller can
determine the location of all end points and accurately calculate the media capabilities of each. In
addition to voice, as the name suggests, the protocol can handle multi-point multimedia
conversations, such as that found in video conferencing.
Management Information Base. Information stored on networks by
high end management systems like HP Openview.
Formed by Bill Gates and Paul Allen in 1974.
-Microsoft lifecycles.
Win 95
August 95
Extended phase
December 00
December 01
End of life
December 02
Win NT3.5
Win 98/98SE
Win ME
August 95
June 98/June 99
December 00
June 03
December 03
Main Phase
Win 2000 Pro
Win XP Pro
Win XP Home
March 00
December 01
December 01
March 05
December 06
December 06
December 01
Jananuary 04
December 04
Extended support
March 07
March 07
December 02
January 05
December 05
Free online
Eight years +
Eight years +
Extended phase - Online support and paid for live support. Patches and downloads only available
on business products.
Non-support phase - No online or live support; only on line self help support available.
End of life - All support ends.
Applications and servers designed to take content from otherwise
incompatible back-end data sources and pass it to Web front-ends
Musical Instrument Digital Interface. The industry standard for the
connection of a musical instrument to a computer.
Mobile Information Device Profile
Multipurpose Internet Mail Extensions. Used for specifying Web
Multiple Input, Multiple Output. Often used in Voice over WiLAN.
Uses multiple aerials and radios to send and receive signals on a single channel - so increasing
bandwidth and range. This takes advantage of multipath signals.
Million Multiply Accumulates
Microsoft Management Console. W2k server
Multimedia Card. - Memory card.
Memory Management Unit.
Multimedia Message Service. Can send photos, voice clips and video
clips. Not limited to the 160 characters of SMS.
MultiMedia Extension. The MMX processor receives audio-visual
data in parallel eight bits at a time, rather than one bit. It also includes a 32KB level 1 cache - twice
the size of the classic pentium.
-MNP Levels 1 - 4
Microcom Networking Protocol. Developed by Microcom Systems
Inc. Enabled error-free async data transmission via a modem.
-MNP Levels 5
As above but also includes a data compression algorithm, which
compresses by 2:1
Microsoft Official Curriculum courses
Modulator/demodulator. A device which allows a PC to
communicate and exchange information with other modem-equiped computers via normal phone
fax operation at up to 14400bps.
1200bps full duplex - can transmit and receive simultaneously.
2400bps full duplex
1200/75bps Prestel
fax up to 9600bps.
9600bps full duplex
Speeds to 14400bps
A flickering effect and is prevalent in screens predominantly
featuring high contrast patterns. The best solution involves decreasing the focus, though altering the
size of the viewing area can help.
-Moire patterns
Seen on monitors and woven linen and silk comes from the french
word for Mohair.
Video Graphics Array
640x480 16 colours.
1024x768 enhanced
8514/A (IBM)
1024x768 (different to SVGA1024)
CRT types Shadow mask - a metal sheet with thousands of fine holes in it, through which the electron beam
passes before striking the screen. It blocks stray electrons increasing image sharpness but reduces
the image brightness. Phosphors on screen shaped as dots
Aperture grill - developed by Sony and Mitsubishi. The stary electrons are filtered out by very fine
vertical wires which preserve the image brightness. Usually have a dark tinted screen which gives a
higher contrast. Phosphors on screen shaped as rectangles/
Refresh rate - aim for minimum of 75Hz.
TFT LCD displays:Image sharper than with CRTs
Bright white fluorescent tubes provide back lighting and transistor driven liquid crystal elements
filter and block the light to produce the image. Can only effectively display one particular screen
resolution - known as Native resolution. Can go below native resolution but loses clarity - cannot
go above native resolution.
-Mono mode fibre
These have inner core diameters of either 9µm and an outer core that
brings the diameter up to 125µm. These only allow a single mode of propagation along the fibre.
Gordon Moore. In 1965 he originated the idea that microprocessor
performance (chip density) should double every 18 months - Moore's Law. Later changed it to a
doubling after two years. Co-founder of Intel in 1968. Intel released the 4004 processor in 1971
with 2250 transistors on the chip. This is dwarfed by the 42 million transistors on the Pentium 4
processor released in 2000.
-motherboard chipsets
Two main chips are involved - called the North bridge and the South
bridge. The North bridge is responsible for the high speed data transfers between the CPU, memory
and the AGP graphics card. It can also have AGP graphics integrated. It also deals with data
transfer to the South bridge. Most current chipsets have a 64-bit interface between the North bridge
and memory.
The CPU front side bus (FSB) speed is the speed at which the processor communicates with the
North bridge and memory.
AGP is an enhancement of the PCI bus, but as it is a point to point connection between the graphics
card, CPU and memory it is a port not a bus. AGP 8x now runs at 533MHz.
The South bridge is responsible for transfers to and from the slower devices such as PCI cards, hard
disks, USB and Firewire devices.
-Mount Rainier
The latest adjustment to re-writeable media. Also known as
CD-MRW. Designed to provide improved packet writing. Also allows CD-RW formatting in the
background and data can be written to the disk straight away. Cluster size reduced to 2KB from
Type: Serial 2-button mouse support, Hosiden connector, IBM PS/2
1 Data I/O
2 Reserved
3 Ground
4 +5V DC (not fused)
5 clock I/O
6 Reserved
Mouse originally conceived by Douglas Englebart at Stanfor University
Multimedia over WAN
Vodaphone's online payment service for transactions between 5p and
£5 via the internet and mobile phones.
MPEG-1 Layer 3. ID3 header information is stored at the end of an
MP3 file (see for more details). The data starts 128 bytes from the end of
the file. Consists of 30 bytes of Track, 30 bytes of artist, 30 bytes of album, 4 bytes of year and 30
bytes of comment.
Motion Picture Expert Group. A compression format for video
enabling high quality picture sequences to be stored on disk. MPEG-1 created primarily for CDROM titles and was designed to deliver full motion video running at 24 to 30 frames per second.
The video image was restricted to quarter screen size of 352 by 240 resolution. The audio
component of MPEG-1 is used for MP3 audio files. MPEG-1 is used for recording video CDs.
The compression standard used on DVD video disks. High quality
video and sound with reasonable file size. Provides broadcast quality video at full motion frame
rates and full screen resolution of 720 by 480. This is the standard format used to create DVD film
titles and is also used in many satellite broadcasting systems. MGEG-2 works by compressing
groups of frames together, rather than treating the video as a series of individual frames. This
makes them difficult to edit.
There are exceptions, but MPEG2 typically breaks frames of video into three different types; I, B,
and P frames. I frames or Intraframes, are the cornerstones of MPEG2 and are the least compressed.
They are created by combining the two fields that make up a PAL signal into a single frame and
applying an algorithm called DCT (direct cosine transform). This is the same algorithm used in
JPEG compression, so an I frame is basically a JPEG picture. Although it is compressed, all the
image data is contained within the I frame subset which allows it to be used as a reference point for
other frame calculations.
The frame is divided into squares called macroblocks, which are then converted into numbers that
represent colour and light values contained in each 16x16 pixel section. The I frames reduce spatial
redundancy, P frames (predictive) reduce temporal redundancy, i.e. pixels that remain the same
from one frame to the next. Preceding frames are scanned for macroblocks that match up with ones
in the current frame. If a macroblock is found that hasn't changed, it is replaced with a pointer that
tells the decoder to repeat the earlier one. Alternatively, if a macroblock is the same but has moved
to a different position (the camera is panning for example) the encoder replaces it with information
that lets the decoder know where the original can be found and in which direction it is going
(vector data). In static scenes, only a few macroblocks will change from one frame to the next.
This allows more data to be discarded and so the P frame can be compressed by as much as 90%.
The B frame (bilinear) describes how the encoder examines areas on preceding and successive
frames to see if anything has changed. This again replaces matching macroblocks with positional
and vector data, but the encoder can also calculate average values from I and P frames, essentially
smoothing out differences between the two. This takes a long time to calculate but can provide
compression up to 98%.
GOP structure (group of pictures) describes the number and arrangement of I, B and P frames. The
default structure for most encoders is a 12 frame GOP, which is IBBPBBPBBPBB before repeating.
This is usually good enough for many video samples. If the video is detailed or fast moving then
this can be shortened to a six frame GOP or less, i.e. IBBPBB. This increases the resolution but
decreases the compression.
Motion Picture Expert Group, audio layer 3. A compression
technology that is applied to music.
The most famous implementation is DIVx. Uses the same GOP as
MPEG1 and MPEG2. Often used by digital cameras to record video sequences.
Message Passing Interface. Used with parallel processing clusters
Multi Protocol Label Switching. A way to keep all IP packets from
the same voice or video session associated with each other in a common "flow", by adding a special
label to the IP packet.
A way of discriminating between packets so that traffic flows can be prioritised. It uses labels, or
tags, containing forwarding information attached to IP packets by a label edge router at the edge of
the network.
Label edge routers perform packet analysis and classification before the packet enters the network
Backbone routers (label switch routers) examine the label and forward the packet without making
forwarding decisions.
Microsoft Point to Point Encryption. Used with PPTP. Based on
RSA RC4 standard and supports 40-bit and 128-bit encryption.
Magneto-resistive random access memory. Non volatile - uses
magnetism instead of an electrical charge to store data. Could lead to instant on computers
Most Recently Used - programs
Multi station Access Unit. A device used in IBM Token Ring LANs
to connect PCs and terminals in a star based topology.
System Configuration Editor. To disable fast shut down run msconfig
and on General page click advanced.
Can edit to change Win95 bootup options.
Scandisk run options on boot-up after improper shutdowns
After prompt
Without prompt
Show screen Win95 logon screen
Do not show
Boot Win95
Run old Dos version
Multi Service Switching Forum. Formed in 1998. Attempting to
redefine switching on WANs.
MicroSoft Intermediate Language. Files are CPU independent and
converted on the fly to run on the target processor by a specific just-in-time compiler.
Multiple Subscriber Numbers
Multi-service Operators - eg telecos providing both TV and phones
Managed Security Services Provider
Mail Transport Agent. (Can be SMTP). Communicates with other
MTAs and DNS. Will queue any mail that cannot be delivered.
Maximum Transmission Unit. Ethernet. The absolute maximum
value is 1500. If the router cannot handle this then the data has to be fragmented increasing the time
Mail User Agent. The mail client used to send and receive e-mails.
A method of transmitting information to more than one target
recipient simultaneously.
-Multi-mode fibre
These have inner core diameters of either 50 or 62.5µm and an outer
core that brings the diameter up to 125µm. There are two varieties, Step Index and Graded Index.
Both allow multiple paths for the waves to propagate.
-Multipartite viruses
Use a combination of techniques to spread itself, the most common
type combines the methods of boot and file viruses.
An operating system feature which allows an appropriately designed
program to run several tasks concurrently.
-MX records
Mail Exchange records. Held in DNS and determines where e-mails
are directed. Can have multiple MX records for a single domain. Useful if one e-mail exchanger
fails. Give each e-mail server a different preference ranking, then is the MX with the lowest
number (the best) is unreachable, the sending SMTP server will run through the list until it finds
one to which the e-mail can be delivered.
MX records should not be pointed directly at an IP address. It is an illegal call and does not work.
The MX record needs to be directed to a specified hostname Formal Qualified Domain Name
(FQDN) format eg which can then be resolved in turn into an IP address.
with the MX10 record being designated to receive all of the e-mails normally.
Open source development of SQL
Negative acknowledgement.
National Audit Office
Network Admission Control, part of Cisco's self defending network
strategy, which uses Cisco's Trust Agent - a client based software agent.
National Access Point. For the Internet. For the UK it is located at
Telehouse in London's Dockland. Throughput around 3Tbps.
Network Attached Storage. Storage devices that attach directly to a
network and not through a server. Known as storage appliances
Network Address Translation. Remotely connected (using Ethernet)
storage, based on servers and RAID arrays. Often carried out by a router or proxy server and
translates a local IP address into an Internet IP address.
Document RFC 1631 defines NAT. Can be provided by either a router or a proxy server.
NAT can be a problem if you want to host a web server. It will prevent any workstation on the
Internet connecting to a web or FTP server on your network that's got a private IP address. The way
around this is to creat a mapped link between the Internet and your LAN using a technique called
'port forwarding'. So for a web server all requests that come into the router on port 80 on its public
IP address are mapped to port 80 of the private IP address of the web server.
-Native Code
A compiled executable in the machine code appropriate for the
particular processor.
Network Basic Input Output System. Developed jointly with IBM
and Microsoft.
NetBIOS Extended User Interface. Best suited to small to medium
sized LANs
Microcode architecture used by Intel on their Pentium 4 and Xeon
Program to gather information on WLans.
Free but only supports the Hermes chipset.
Network operating system from Novell Inc.
cache engine
public web servers
video streaming
desk tops
-Network Layer
Layer 3 in the OSI model; the logical network entity that services the
transport layer; responsible for ensuring that data passed to it from the transport layer is routed and
delivered through the network.
-Network topology
The physical and logical relationship of nodes in a network; the
schematic arrangement of the links and nodes of a network. Networks typically have a star, ring,
tree or bus topology or some combination.
Near End Cross Talk. The interference between two pairs of cables
used for transmit and receive. NEXT, the ratio of interference to transmitted signal, both measured
at one (near) end of a terminated cable.
Near Field Communication - developed by Philips and Sony. Allows
transfer of data between their products. Carrier Frequency 13.56MHz. Distance up to 20cm and
data rates of 212Kbps
Network Interface Card.
Network Information Centre. The people who register your domain
National Infrastructure Security Co-ordination Centre. Collated
software bugs for the government.
National Land Information Service
National Land and Property Gazetter
A hardware device at which two or more communications lines meet.
Each computer or other device on the network
The registry for .uk domain names.
Network Operating System.
Network Operations and Service Centre
To save files with a different extension to .txt, use Save As and put
the complete file name in inverted commas.
Network processor Modules.
Network Processor Unit
Non Recurring Engineering
Non Return to Zero. Binary coding transmission with no return to
neutral state after each bit is transmitted
A device that converts the phone company's 2-wire ISDN U interface
to a 4-wire S/T interface for compatibility with customer site terminal adapters.
New Technology Filing System
NT file system for windows 2000
Network Time Protocol - RFC 1305
National Television Standards Committee. American video standard.
Videos play at 30 frames per second.
Network Termination Unit.
-Null modem
A device that connects two DTEs directly by emulating the physical
conditions of a DCE
Non-Uniform Memory Access - a type of parallel processing
architecture in which each processor or small group of processors has its own local memory but can
also access memory owned by other processors.
The nominal velocity of propagation of a cable is the speed that a
signal passes along a cable as a percentage of the speed of light. Many NVPs are between 60% and
No eXecute. Built into AMD 64 bit processors. Limits a buffer
overflow attack possibilities, which is where the computer's buffer memory space is overwhelmed
with data and so can be made to execute malicious code.
Optical add-drop multiplexer. An optical extension of a common
SONET element called add-drop multiplexer, this is a piece of equipment that allows wavelengths
to be added or dropped at particular node points.
Open Exchange's electronic invoice delivery service which has
received Custom and Excise agreement to stop printing out invoices for VAT records.
-Object code
The compiled version of the source code written in machine code.
-Object Orientated
A language that lets you encapsulates program elements as objects.
Open Database Connectivity. Designed to present a programming
interface to application programs that is independent of the underlying database implementation, i.e.
an application can talk to a database connection and not know what the underlying database
implementation is.
Open Directory Project
resources for many large sites, eg google.
powers core directory
Orthogonal Frequency Division Multiplexing. Uses multiple carriers
to increase data rate on Wireless connections.
Office of Government Commerce
Open Host Controller Interface. Used on Firewire.
Optical Image Stabilisation. Used to reduce camera shake in
camcorders. It uses motion sensors within the lens itself. When these detect camera movement,
they trigger a small actuator that makes tiny adjustments to an internal lens, redirecting the
incoming light and helping to reduce camera shake. Also see DIS
On Line Analytical Processing. Developed by Ted Codd.
Object Linking and Embedding. Connects data between two files.
Data in a linked destination file automatically updates when changes are made to the source file, but
does not duplicate the information which is in that file. Embedding, on the other hand, creates a
copy of that information (so using up hard disk space). Modifying data in the destination file does
not affect the source file directly.
Open Mobile Alliance.
Open Mobile Application Processor Interfaces. - offers access to any
service on any network using any kind of mobile terminal.
-Open Access Internet Time Servers. - UK
-Open Air
Wireless standard 1.5Mbps.
In Windows Applog folder. Records the frequency with which
programs on a PC are used.
Object Request Broker - Allows communication between objects of
independent language or platform
Office Startup Application. Carries out initialisation tasks to help
office load faster
Open Standards Fabric Initiative. Formed by five leading Fibre
Channel switch makers.
Open Systems Interconnection. An open systems architecture
developed by the ISO to provide a means by which many different sorts of systems can
communicate together efficiently and economically.
-OSI Model
Open Systems Interconnection Model. A seven layer model defining
the way systems communicate. Provides a structure into which internationally agreed standards can
be fitted. Each layer represents a function or group of functions from the 'Application' layer (7) that
provides a 'window' for the operating system, to the Physical layer (1) that provides the transmission
Layer 1
This layer puts raw data over the communication channel. This layer
is largely responsible for the mechanical, electrical and procedural
Layer 2
Data link
This breaks the data up into frames instead of sending it as one long
stream. Frames are transmitted in sequential order and
acknowledgement frames returned to prove receipt of data. It is up to
the data link layer to solve problems caused by damaged, lost and
duplicate frames. Also used to deal with transmission rate problems
where a fast transmitter floods a slow one
Layer 3
This controls the operation of the subnet and is mainly concerned with
routing packets. Can be based on static routing tables or determined
for every packet. Also has facilities for providing billing information
to enable operators to charge for network usage.
Layer 4
Provides a method of communication between the session and
network layer. It takes data from the session layer, breaks it into
smaller units and passes them onto the network layer, making sure
that the pieces arrive in the right order at the other end. It is an endtoend layer; an application on the source machine has a conversation
with an application on the destination machine using the message
headers and control messages.
Layer 5
Allows machines to set up sessions between themselves. Also an
end-to-end layer. A session performs tasks such as transferring a
file. It manages the dialogue by specifying if the conversation can
occur in both directions at the same time. If not it manages whose
turn it is. The session layer also has to cope with synchronisation in
the case of a system crash - so allowing file transfer to continue from
the point it left off.
Layer 6
Layer 7
Deals with data syntax and semantics, e.g. encoding data.
Contains a variety of protocols for communication - mapping user
commands onto real protocols.
(Session and Presentation layers rarely used by any applications).
Each layer has its own header and the payload of the higher layers.
The Internet Protocol Layer 3. The header contains the source and destination address plus the
Payload (i.e. layer 4 and above).
Layer 4 protocols.
UDP User Datagram Protocol: Only added value is addressing of ports on host.
TCP Transmission Control Protocol. Connection Orientated - establishes a connection between the
two hosts.
Each packet has about 40 bytes of header information. Layer 3 (IP) header is 20 bytes, 8 from layer
4 and 12 from layer 5.
Overscan protection
Open Shortest Path First. A protocol used by routers on an IP
network. Now being used in preference to Routing Information Protocol (RIP) which is an ageing
protocol. It is used when a router detects a change in the network. The change is automatically sent
to all machines in the same network to keep routing tables updated and identical across the network.
OSPF only sends the specific changes and only does so when the changes occur, not every 30
seconds like RIP.
Optical Time Domain Reflectometry
Open Trading protocol. Backed by Mastercard, Digicash and
Netscape - aims to produce a consistent web based environment for e-commerce transactions.
One Time Programmable
To export to Outlook 2000 and XP use the backup add-on from
Optical Cross-connect. This is the true system level optical switch,
employed primarily in long distance networks, that can shift services from one wavelength to
another, thus representing a key target system to utilise a tuneable laser
Peer to Peer
Old 423 pin New 478 pin
Intel's code name for the MMX processors.
This is a unit of data, which is typically a part of a file, prepared for
transmission across a network. Has the following sections.
Start delimiter
Destination address
Source address
Type of data
Data (length)
CRC (error checking)
End delimiter
Phase Alternating Line. Videos play at 25 frames per second.
Microsoft Security Offering. Relies on Trusted computing
Personal Area Network.
-Parallel Port
A plug and socket connection that can transfer a complete byte at a
time. Speeds range from 40Kbytes/s to more than 1Mbytes/s.
25-hole female connector.
Four types of parallel ports, unidirectional, bi-directional, EPP and ECP. To check which modes
are supported, look in the peripherals section of the PC's Setup program.
Unidirectional or SPP. Data flows outwards only at 40-50Kbytes/s.
Bidirectional. Two way communication at around 100 - 300Kbytes/s.
EPP Enhanced Parallel Port. Transfer rates of around 400 - 1000Kbytes/s. It provides the best
possible performance that the port has to offer. When selecting EPP in System Setup, choose
version 1.9 if possible.
ECP Enhanced Capabilities Port. Improves both speed and two way communication between
device and computer. When selecting ECP in System Setup, you will be able to select a DMA
channel. Avoid conflicts by checking device manager for free DMA channels. If you can't fix the
conflict use bi-directional mode.
Standard Parallel Port Resource Settings.
out H378
out H278
25 -way female D-type connector
D0 (I/O)
D1 (I/O)
D2 (I/O)
D3 (I/O)
D4 (I/O)
D5 (I/O)
D6 (I/O)
D7 (I/O)
-ACK (I)
PE (I)
18 - 25
-Parity Bit
A bit that is set to "1" or "0" in a character to ensure that the total
number of "1" in the data field is even or odd as desired.
-Parity check
The addition of non information bits to make up a
transmission block that ensures that the total number of "1"s as always even (even parity) or odd
(odd parity). Used to detect transmission errors.
Partial Attribute Set - part of Active Directory.
Adding a three character password before executing the rest of the
batch file. Save the following text as Getkey.scr, making sure to include the blank lines before
RCX and after Q:
A 100
INT 16
Now enter the command Debug&It;Getkey.scr to create Then place in a
folder on your path. Getkey waits for a keystroke and returns the corresponding ASCII code. The
following batch file uses Getkey to detect the passwprd AOK (case sensitive).
ECHO Enter password.
ECHO ***
IF '%K%'=='xqj' GOTO OK
ECHO Password OK
Consult an ASCII table and change the numbers to select a different password.
-Password XP
To remove passwords. Create a bootable floppy or CD.
Use the offline NT Password and Registry editor (
Create bootable disk and follow the instructions.
Packet Binary Convolution Coding. Texas Instruments solution to
Private Branch Exchange.
IBM's version of MS DOS.
Peripheral Component Interconnect. This is the standard bus design
for computer motherboards and expansion slots that can transfer 32 or 64 bits of data at one time.
-PCI Express
Serial bus - needs new cards. Offers increased bandwidth up
to 80Gb/s. Enables direct connection to high bandwidth adaptors without the expense of an added
I/O bridge chip.
Intel chipset named Lindenhurst for servers and Turnwater for workstations.
Parallel bus - accepts older cards
Printer Control Language. Used by HP with its laser printers. The
information, resolution, typeface and paper size are transmitted to the printer, which interprets the
instructions and converts the data into a raster or bit mapped image, and the image is then printed
out. Hence the need for a powerful CPU and generous amounts of memory in a conventional laser
More commonly known as a PC card, expands a computer's
capabilities via a credit-sized card connection. Mainly used on portable computers. Personal
Computer Memory Card International Association. Founded in 1989. The standard features:
68 circuit pin and socket,
5.4 by 8.6cm
1.27mm mating interface,
5V working,
Polarisation key for correct insertion,
3 mating pin length (first mate last break) (3.5/4.25/5.00mm),
10000 mating cycles.
There are three physical sizes of cards that differ only in thickness: 3.3mm, 5.0mm, 10.5mm.
Type 1 cards, RAM, flash memory etc,
Type II cards, IO devices,
Type III cards Hard drives, radio comms devices etc.
Can interface with both 8-bit and 16-bit buses.
Support physical access to up to 64MB of memory.
People Can't Memorise Computer Industry Acronyms.
Phase Change Rewritable - A rewritable CD in which the laser
momentarily melts the crystalline coating on the disk, which then quickly cools to form an
amorphous spot with lower reflectivity. To erase the data, a medium power laser beam can be used
to cause re crystallisation.
Personal Digital Assistant.
Page Description Language
Protected Extensible Private Network
Interconnections between networks, usually on an ISP level. Good
quality peering means better Internet access for the end user
-Peer to peer
Links computers together, but has no central server.
Launched in 1993 by Intel to replace the 486. The first Pentiums were
made with 0.8 micron (800nm) technology and had 3.1 million transistors operating at 60MHz.
There were four architectural changes Pentium Pro, II, III, and IV and ended with one version pf the
P4 called 'Cedar Mill' built with 65nm technology that has 188 million gtransistors running at
3.6GHz. All new chips will be called 'Core 2 Duo'.
-Pentium 4
Early ones used a 423 pin socket, but the newer ones use a 478 pin
Practical Extraction and Report Language. A high level language
derived from a wide range of sources including C and the UNIX shell. Can be downloaded free
Created by Larry Wall in 1987 but has been developed by a global community. Current version is
Packet Flow Acceleration.
Attempts to trick recipients into revealing passwords and bank details.
PHP Hypertext Preprocessor. A scripting language used for
developing dynamic web pages and sites. Typically used on Solaris and Linux platforms.
Originally written in 1994 and completely rewritten in 1997 by the founders of Zend.
A similar practice to hacking but where telephone calls are made on a
PBX system that bypasses the charging system.
Physical layer Device
-Physical layer
The lowest (first) layer in the OSI model; responsible for the physical
signalling, including the connectors, timing, signal forms and other related matters.
Pairs in Metal Foil cables are a type of shielded cable where each of
the individual pairs are contained in a foil sheath. This type of cable provides maximum isolation
between the individual pairs, or minimum cross talk losses. Cat7 cables are PIMF cables with an
additional overall shield, usually a braid.
Packet InterNet Groper. Written by Mike Muuss. A way of
measuring the Internet's performance between yourself and Internet sites. Results usually expressed
in milliseconds. To use click Start, Run and type ping server. e.g. ping
The ping command is used to send an ICMP (Internet Control Message Protocol) echo request
message to a target host. It sends a packet from one device, attempts to bounce it off another and
listens for the reply. A prompt reply means that the bit of the network between pinger and pingee is
To test a PCs loopback address - a virtual IP assigned to all NICs when TCP/IP is installed. Its IP is
always the same - Pinging this address from the PC shows that the NIC is configured and
Ping normally only sends four packets by default. The Ping command has the -t parameter
thatconfigures it to continuously ping the target device ping -t To pause it and display
the statistics press Ctrl Break and to end it press Ctrl C
Testing DNS can be done by pinging the name of a remote host eg ping
Even if the DNS server does not respond to ping requests the result will still give the IP address for
that URL, which tells you that the DNS is working.
Public Key Cryptography. Works by: when the cryptography
software is first set up it generates a pair of keys. One is a private key which is kept secret and
guarded with a password phrase. The other is your public key which can be distributed widely.
Ideally others should sign it digitally to ensure that messages do not become corrupt. The public
key is used for encryption and signature verification. The private key is used for decryption and
signature generation. Two examples of these are Turnpike and PGP (Pretty Good Privacy).
Public Key Infrastructure.
-Plasma Screens
Consist of two thin layers of glass between which is a mesh of minute
pockets of compressed gas - pixels. Each of these pixels have sub-pixels, or phosphors in the three
primary colours, each of which is individually controlled. When the gas is electrically charged it
turns to plasma and UV light. The reaction of the UV light with the phosphors causes the coloured
light to be emitted. Produces a high contrast, fast picture. Susceptable to screen burn and get hot.
Physical Layer Convergence Protocol. Used in IEEE802.11b
-Plenum Cables
Used in the space above false ceilings or below an access floor.
Produces very low levels of toxic fumes when burnt. Often coated in Teflon.
Physical Media Dependent
Polarisation Mode Dispersion 40G optical fibres
Portable Network Graphic. Invented by vendors in 1995 to avoid
paying royalties to UNISYS for .gif technology. Offers better compression than GIF, a far wider
colour spectrum and supports variable transparancy.
Power Over Ethernet - IEEE802.3af POE hubs send out a pulse at
20mW and 802.3af devices will deflect back with a 25k resistor built into the port. If the signal is
not deflected, the hub will not attempt to deliver the full power. The absolute maximum power per
port is 15.4W at 48Vdc.In practice, the maximum power is 12.95W, limited by the resistance of the
cables. Can be provided over CAT5 and CAT6 cable for up to 100m.
POE also referred to as Data Terminal Equipment (DTE) Power via Media Dependent Interface
Power over Ethernet Plus, IEEE802.3at is being considered and is expected to be ratified in 2007. It
is likely it will deliver at least 30W.
Windows 95 and 98 policy editor. Found on W95 and W98 CDs in
\tools\reskit\netadmin\poledit. Run poledit.exe, double click Local User, System, Restrictions and
check Only run allowed Windows applications. Click Show, then Add and enter the executable
filename of each program. Better to run Poledit from a separate disk or any one can then alter files!
A communications technique that determines when a terminal is ready
to send data. The computer continually interrogates all of its attached terminals in a round robin
sequence. A terminal acknowledges the poll when it has data to send.
Point of Prescence. The location of the nearest node for an ISP, this is
the number dialled to connect to the Internet.
The Post Office Protocol (version 3) is the most widespread Internet
standard for e-mail software to retrieve messages from a mailbox held on a mail server. E-mails are
stored on a POP3 server at the ISP and then down loaded into and read by a POP3 client e.g. the
Bat! or Outlook Express.
-Polymorphic virus
Changes itself each time it spreads. Because polymorphic viruses'
signatures change, usually randomly, the common signature scanning techniques often fail to find
them, antivirus packages must rely on heuristic technologies to detect them.
Used for connection requests and exchange of data with servers. If
the IP address is considered to be the country, county, city street and house number, then the port
can be considered to be the intended person in the house, e.g. Mr Smith. There are 65535 possible
ports. The first 1023 are the system ports and will generally be used by root processes or programs
executed by privileged users.
The port is the addressing mechanism used in both TCP and UDP. It identifies the process on a
system addressed by the IP address to which the TCP segment or UDP datagram should be
Number of ports can be doubled using UDP (User Datagram Protocol)
Port 21
Port 23
Port 25
SMTP Send Mail
Port 53
DNS Name Service
Port 80
Port 110
POP3 Retrieve e-mail
Port 111
Port mapper service
Port 119
Port 123
NTP Network Time
Port 135
Windows Messenger Service
Port 135
DCom services, RPC
Port 137
NetBeui, Also Windows Messenger Service, RPC
Port 138
Windows Messenger Service
Port 139
NetBeui, Windows Messenger Service, RPC
Port 443
Secure web HTTPS
Port 445
Windows Messenger Service, Microsoft Cifs file sharing
Port 1433 SQLsnake a SQL worm infecting SQL servers.
Port 1434 SQL server
Port 1494 Citrix Meta frame
Port 3128 Web cache
Port 3389 MS Terminal Server
Port 5190 AOL
Port 6667 IRC Internet Relay Chat
Port 8080 Web cache
Port 17300 Kuang2 back door
1234, 2773, 6713, 7215, 27374, 27573, 54283
Back Orifice
8787, 31337, 31338, 54320, 54321.
A good list of Trojan ports can be found at
To obtain a list of listening ports - type netstat -a
-port forwarding
when a port on a router is opened and then assigned a specific IP
Power On Self Test. The first process a PC runs when it is switched
on which checks memory, processor, graphics etc. A series of beeps indicates if errors are found.
One beep usually means that all is well.
The leading alternative database to MySQL in the LAMP open source
development and deployment platform. It focuses on providing rich features and standards
compliance. It is becoming a serious option for enterprise databases. It began in 1986 at the
University of California, Berkley. Its original author was Michael Stonebraker, the creator of the
Ingres relational database management system. Postgres means "after Ingres".
A page description language developed by Adobe Systems that
describes each element as a vector pair, rather than telling the printer where to place each dot of ink
or toner. It is more suited to graphics printing and has wider applications than PCL as it can
produce better quality output at higher print resolutions.
Applied to NEXT and ACR. Used to make measurements when
data transmitted on all four twisted pairs.
(  dB )n
PSNEXT  10 log 10  10 10
n 1
Power demands.
Low end CPU
Mid range to high end CPU
PCI graphics or sound card
Low to mid range graphics card
High end graphics card
IDE hard disk
Optical drives
Partial Private Circuits - last mile hardware connections for
broadband connections
Plastic Pin Grid Array - used for Celeron chips with integrated level 2
cache memory. Socket 370.
Point to Point Protocols.
Point to Point Tunnelling Protocol
Primary Rate Interface
Microsoft - VPNs
Toner a health hazard. Clean up with a cold damp cloth. Not vacuum cleaner or hot water (melts
Alternative drivers on the W95 CD in Drivers\Printers\etc.
There is also the Enhanced Print Trouble-shooter tool epts.exe on the W95CD in Other\Misc\Epts
Inkjet Printers.
Developed in early 1980s. Canon invented the technology and was the first to produce a 'BubbleJet'
cyan, magenta, yellow and keystone black.
Inkjets use one of two methods to eject the ink from the cartridge, either they heat the ink or they
use a crystal to squeeze out a single drop. Both methods use similar cartridges, with a well for the
ink and a head for each colour, made up of around 50 nozzles through which the ink is dropped.
With the heating method, a small resistor within the nozzle is heated. This heats the ink to around
100oC and as the ink expands, a drop is squeezed out of the nozzle and onto the page. The ink has
to be heated and cooled thousands of times per second, so it must remain the same consistency
under heat.
The other method, known as piezo electric technology, uses a crystal instead of a resistor. Again, it
sits in the nozzle acting a little like a valve. A small electric charge is applied to the crystal and the
crystal twists, releasing a small drop of ink onto the page. Epson is the only manufacturer to use
this technology
Photo printers will generally use more than the four colours, CMYK, using instead six or seven
inks. They will always include light cyan, and light magenta. Canon also includes a second shade of
This is the process which uses dots in patterns to create different colours.
Half toning.
This process involves laying down larger or smaller dots to create a more
realistic image
This is when the printer misaligns the lines of print, leaving out a small
amount of the page, which shows through as a thin white line.
-Print folders
Create the following batch file called dirprn.bat using
Notepad and save in Windows folder.
notepad /p \dirlst.txt
del \dirlist.txt
In Explorer find the batch file, right click it and choose Properties. Click on the Program tab.
Change the Run Option from Normal window to Minimised. Check the box for close on exit.
Click OK to close the Properties dialog box. In Explorer now select View, Folder Options. Click
the File Types tab. Select the Folder file type and click the Edit button. In the Edit File Type dialog
box, click New. For Action enter Print. For Application used to perform action enter
Close all of the dialogue boxes with OK. When you right click on a folder or drive icon in
Explorer, you should find a Print option in the pop-up menu.
-Print Server
Manages access to shared network printing resources.
32 bit 80x86 can only address 4GB of memory unless bank switching
is employed.
1984 Bill Joy and Dave Patterson start working on RISC processors.
1985 Intel introduces the 386 microprocessor
1987 The first SPARC processor is born.
1991 Intel introduces the 486SX.
Texas Instruments release the SuperSparc.
MIPS Technologies introduce the R4000.
1992 Digital launches the Alpha
1995 Sun introduces its first 64-bit processor, the UltraSparc.
Intel releases the Pentium Pro.
1997 Intel Pentium II and Xeon released.
1999 AMD introduce the Athalon, Intel releases the Pentium III
2000 Transmeta launches the Crusoe.
Intel releases the Pentium 4
IBM introduces the Power4 chip
2001 Intel releases the Itanium.
The Itanium breaks away from the 80X86 instruction set. It uses a new instruction set called EPIC
(Explicitly Parallel Instruction Computing) and can perform a number of tasks within a single clock
cycle. It can address significantly more memory than 32 bit processors.
Used in Bluetooth to define certain applications, such as file transfer
or headset communications. Two Bluetooth devices need certain profiles in common to work
-Promiscuous mode
When a network adaptor processes all received frames. Used in
The rules that govern computer communication
-Proxy server
A server that sits between the browser and a Web server, which
monitors all requests that pass through it. The proxy server intercepts all requests and checks that it
does not already have the requested page stored on the hard disk. If it has, then the proxy server
returns the requested Web page from its own hard disk. If the proxy server doesn't have the
requested page, then it forwards the request to the web server. Proxy servers speed up internet
access for large numbers of users, and can also be used by companies to filter out requests for
unsuitable web pages.
Partial Response Maximum Likelihood. An advanced detection
method used on hard drives heads to improve data transfer rates and increase how much data can be
stored on a drive's platter.
PowerSum for ACR
PowerSum for ELFEXT
PowerSum for NEXT
Public Switched Telephone Network. A circuit is dedicated
for the whole time of the call whether information is being sent or not. Restricted to the frequency
range of 300Hz to 3200Hz as it is all that is needed for voice.
Public Telecommunications Operator
Personal Video Recorder
Pre boot eXecution Environment. Part of Intel's open wired for
management specification that automates client management. It allows a PC to boot remotely from
an image stored on a server. PXE has a wake-on Lan element that allows an administrator to
remotely power a computer by sending a signal to the network card.
Based on CompactPCI. The specification was ratified in
August 2005. Uses the same standard mechanisms defined in the PCI plug-and-play specification
for device discovery and configuration. The basic physical layer consists of an ac coupled LVDS
pair for RX and TX and utilises 8b/10b encoded and de-emphasis. The transmit and receive pair
together are called a lane. The initial speed of 2.5Gb/s provides a nominal bandwidth of 250MB/s
in each direction per PCI Express lane. This rate represents a two fold to four fold increase over
most regular 32-bit 33MHz devices, and unlike PCI where the bus bandwidth was shared among
devices, this bandwidth is provided to each device. The controller is capable of supporting up to a
x16 PCI Express link plus a x8 link providing a total of 6GB/sbandwidth to the PXI backplane,
which is a 45 times improvement in PXI backplane throughput.
Screen 12, VGA screen. Q basic program from Maxim Elektor July/
August 2000, page 35
Quarter Common Intermediate Format - Video compression
Quarter Inch Tape. Back-up tape format. Stationary read/write head,
tape speed can be up to 120in/s. Data is written to one of 44 straight tracks in one direction before
the mechanism reverses and records information on a parallel track in the opposite direction.
Storage capacity depends upon the length of the tape. Access times are slow but data transfer rates
can be up to 6Mb/s
Quality of Service - a term used to describe the performance
properties of an ATM service, especially guaranteed throughput level.
keyboard layout designed in 1868 by typewriter inventor Christopher
RAID Advisory Board
Remote Access Concentrator
Rapid Application Development. Combine together pre built
components with just a bit of extra code. Microsoft.
Remote Authentication Dial In User Service. part of W2k VPN
Rate Adaptive ADSL - manages to provide a connection over a
greater distance than standard ADSL - 5.5km rather than 3.5km
Redundant Array of Inexpensive (or Independent ) Disks. Some
redundancy of storage space. Many RAID controllers offer a large data cache.
Level 0 simple data striping. The storage strategy involves combining multiple drives into a single
logical data volume. The data are then interleaved among multiple disks. Having multiple drives
service data yields an increase in performance over non-array disks because the data is being written
in parallel.
Level 1 data mirroring. This level of RAID involves a redundancy of storage devices. Data are
written to two separate disk drives. If one fails the other is available to service data requests. Good
data protection, but doubles the number of devices needed.
Level 3 involves data striping as does level 0, but uses an additional device (drive) to hold parity
information that can be used to reconstruct the data stored on any of the other storage devices. The
overhead of RAID level 3 introduces a performance penalty that makes it unsuitable for
applications with intensive I/O activity.
Level 5 also uses parity to reconstruct data on a failed drive, but distributes the parity information
on the data drives. Provides better performance than RAID 3, needing less hardware, but is still
slower than RAID 0.
Level 6 designed to accommodate the loss of two drives simultaneously, or to handle a disk failure
during a data rebuild after an initial failure
PC-DOS version of MemMaker
RAM digital to analogue converter oversees the data transition from
graphics card to screen.
Reconfigurable Algorithm Processing
Reverse Address Resolution Protocol. Used to give a machine an IP
address when it knows its Ethernet address. This is often the case when a diskless workstation
boots up. In this case a RARP server responds to the request and gives the machine its IP address.
However RARP broadcasts only reach as far as the router. This means that the requesting station
has to be on the same network as the RARP server. A better protocol is to use Bootp, which uses
UDP to span routers. Bootp also sends out additional information including a file to boot from, the
IP address of the default router, and the subnet mask.
Remote Access Server
-Rat Attack
Remote Access Trojan attack e.g. Back Orifice
Real Animated Vector Effects
An image format, which is essentially a copy of the uncompressed
image data produced by the camera. Large file size.
Real-time Control Protocol - used in VoIP. Complements RTP by
monitoring the quality of the end to end link.
Relational DataBase Management System
Resource Description Framework - method of processing meta data
on the web i.e. data about data. e.g. Intelligent bookmarks that update in tandem with the site
Remote Data Memory Access. Used in SANs
Rambus Dynamic Random Access Memory. Favoured by Intel.
Lower cost alternative to DDR RAM. It has four power modes:
Power Down mode uses no energy at all,
Nap mode uses very little power,
Standby mode uses about 20% of the power used when it is in its active state or Read/Write mode.
Originally developed using Rambus signalling levels (RSL) to provide faster operating speeds than
available through DRAM devices.
-Recovery Console
A row in a database table.
Use when XP will not even start in Safe mode.
-Refresh rate
How many times per second the image is updated on a monitor. Aim
for at least 75Hz or preferably 85Hz.
-Registered Owner
folder. Two separate entries - Registered Owner and Registered Organisation. Double click to edit.
Microsoft reg clean utility. Removes unused or corrupted registry
Registry clean utility -
File system.1st in the root directory a copy of the registry exactly as it was when Win95 was first
installed. To copy it attrib -h -s -r system.1st
Copy it to the Windows directory (copy c:\system.1st c:\windows)
attrib -h -s -r system.dat and then delete it
rename the copy of system.1st as system.dat and reset attributes as attrib +h +s +r system.dat
Back up registry files, system.dat and user.dat. You cannot use Explorer or DOS to copy these
files. Use cfgback.exe on W95CD\other\misc\cfgback folder. Copy cfgback.exe to c:\windows
and then copy cfgback.hlp to c:\windows\help. To make a backup double click cfgback.exe and
follow instructions.
Registry editing. A Registry entry is called a key.
Back up system.dao, system.dat, user.dao and user.dat.
Choose Start, Run, type regedit.exe in the Open box. Press Ctrl and F, and in the 'Find what' box,
type in the name of the errant driver, without the .vxd extension. Now make sure only Keys is
checked in the 'Look at' section, and click Find next. You should land on a folder under
hkey_local_machine\system\currentcontrolset\services\vxd. Triple check that you have highlighted
the correct Registry key before pressing the Del button and exit the Registry Editor.
Each time Windows starts it creates a backup copy of the registry, system.da0 and user.da0. To
restore them get to the command prompt in safe mode, then type
attrib -s -h -r *.da?
ren system.dat system.tmp
copy system.da0 system.dat
ren user.dat user.tmp
copy user.da0 user.dat
Then restart the computer.
Windows 98 does not create .dat files as it uses a different system for creating Registry backups.
The W98 registry checker keeps several backups in the hidden SysBckup folder (in the Windows
folder). These are named, etc. When the registry checker adds a new backup it
deletes the oldest.
Restore registry in W98, run c:\windows\scanreg.exe/restore
Internet sites visited - hkey_user/software/microsoft/internetexplorer/typedurls
Disconnected IDE often a cause of missing CD drive - hkey_local_machine\system\current
controlset\services\VxD\IOS. If it contains an entry NoIDE, then delete and reboot. The machine
will redetect the IDE channel. Some viruses will also hide the CD.
Registry entry for CD drive letter
Double click source path.
To optimise the registry: First run Regclean. For W95 make a batch file containing
regedit /e temp.reg
regedit /c temp.reg
Store as smallreg.bat and run in DOS. Can take a long time.
W98 start in DOS and type scanreg /opt.
WME Create startup disk. Restart using disk. Select minimal boot. At DOS prompt type
scanreg /opt
Win XP To back up the Registry run Regedit and then File, Export and give the Registry backup a
Removing trojan etc:Hkey_Classes_Root\exefile\shell\open\command
Both of these keys should only contain the entry"%1" %*
Other keys to check:Hkey_Local_Machine\Software\Microsoft\Windows\CurrentVersion\RunServices\
Hkey_Local_Machine\Software\Microsoft\Active Setup\Installed Components\KeyName\
Remove all references to trojans etc.
Also check win.ini files and system.ini files. In win.ini look under RUN= and system .ini shell= in
the [boot] section, which should just contain the line explorer.exe if anything. (Start Run Sysedit )
Check for Run and Run Once:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run and RunOnce
A device used to extend transmission distances by restoring signals to
their original size and shape. Typically used within Ethernet networks to extend segment lengths.
Repeaters function at the physical layer in the OSI model.
Ensuring that there are no single points of failure. Often done by
using multiple servers, firewalls, switches etc so that there is always backup in case of problems
-Resource monitor:
Monitors System, User and GDI. These memory areas are only used
by 16 bit software. Resources for 32 bit software not restricted.
Radio Frequency IDentification
Thin Coax. Cheapernet. RG58A/U and RG58C/U. 50 ohms  2
ohms. Minimum propagation rate of 0.65c. and minimum shield coverage of 95%.
Rambus Inline Memory Module. Also known as RDRAM. This
memory has the potential to run at speeds of up to 800MHz as opposed to SDRAM's maximum of
133MHz. Speed is also increased by processing instructions 16 bit at a time rather than 8 bit. Any
unused RIMM slots require a CRIMM (Continuity RIMM) to be installed - basically a blank that
completes the circuit.
A network topology in which each station is connected in series to
form a closed loop.
Routing Information Protocol. See OSPF.
Regulation of Investigatory Powers Act 2000.
Recognises that some actions which are essential to keep a network functioning may result in
communications being seen by the network operator, e.g. re routing of incorrectly addressed emails.
The Act makes clear that users of networks should expect such actions to take place routinely; there
being no requirement on the network operator to give warning of the possible loss of privacy.
Organisations may also examine activity on their own networks for some business purposes.
However, before this may be done, all users must be informed that their communications may be
monitored. The Lawful Business Practice regulations supporting the Act set out the purposes for
which monitoring may be used. These include ensuring compliance with acceptable use policies
and other organisational rules, but only after users have been informed of the rules in advance.
Warn staff if and when they are being monitored.
Warn people e-mailing your company that e-mails may be monitored.
Regularly inform staff about what is being monitored.
Only monitor staff covertly with police involvement.
Réseaux IP Européens - a collaboration between European network
operators using the TCP/IP suite of protocols to deliver Internet services.
The process of changing data from one form to another. Often used
for changing CD music files (.cda) to .mp3 files.
A remote installation wizard for Windows server operating systems.
Remote Installation Services - part of PXE
Reduced Instruction Set Computer.
Registered Jack
8 way modular FCC connectors. Wired to schedule 258A, 10BASE-T
Pin No.
Pair ID
Colour / Tracer
White / Orange
Orange / White
White / Green
Blue / White
White / Blue
Green / White
White / Brown
Brown / White
Pair 3
Pair 2
2 3
4 5
Pair 1
4 5
Pair 4
6 7
Socket front
Return Loss is the difference between the power of a transmitted
signal and the power of the signal reflections caused by variations in the channel impedance. High
return loss values mean a close impedance match, which results in a large difference between the
powers of transmitted and reflected signals
Radio Lan. Contains the HIPERLAN. Uses frequencies in the range
5.150GHz and 5.875GHz. Divided into three bands.
Band A 5.150 to 5.350GHz
Band B 5.470 to 5.725GHz
Band C 5.725 to 5.875GHz
Reduced Latency DRAM
Rights Management Services - MS Windows 2003 server. It allows
you to encrypt documents and e-mails on your network and to have full control over who can read
them and what they can do with them. Can also be applied to e-mails to stop them being forwarded
Restriction of Hazardous Substances - at the heart of the WEEE
Return On Investment
Read Only Memory.
-Root directory
Maximum number of entries is 512. Long file names take up
additional entries.
A device used for communications between two networks. They
function at the network layer (3) of the OSI model and can determine the best route to send data. In
a packet switching network, such as the Internet, a router is a device which examines packets of data
and sends them to their appropriate destination.
Routers provide access control. They will pass on packets to a destination only if they have a rule
that says that they can. They stop broadcasts across networks. Allow departments of a network to
be placed on separate subnets - making management and fault finding easier.
Remote Procedure Call. Methods for objects to talk to each other. It
allows a program that is running on one computer to seamlessly access services on another
computer. Uses ports 135, 137 and 139.
Regional Playback Control. Used on DVDs. Allows region
information to be set up to five times before your drive is locked to the last setting.
Region 0
Region 1
Region 2
Region 3
Region 4
Region 5
Region 6
Region 7
Commonly used to describe no region locking
Canada, US, US Territories
Europe, Japan, Middle east, South Africa
South east Asia, Taiwan
Australia, Caribbean, Central America, Mexico, New Zealand, Pacific Islands,
South America
Africa(part), India, Pakistan, Russian Federation
Region 8
Special International venues, i.e. aeroplanes, cruise ships etc
Often PC DVD drives are not region protected but the MPeg2 decoder cards and software players
Routing and Remote Access Service. W2k VPN. Also part of
Windows Server 2003 - built in network layer firewall.
EIA interface standard between DTE and DCE, employing serial
binary interchange. The industry's most common interface standard.
-RS-422, RS-423
EIA interface standard that extends transmission speeds and distances
beyond RS-232/V.24. RS-422 is a balanced voltage system with a high level of noise immunity,
RS-423 is the unbalanced version
EIA general purpose 37 pin and 9 pin interface for DCE and DCE, employing serial binary interchange.
Balanced interface similar to RS-422 but using tri-state drivers for
multidrop applications.
Robust Security Network, a WPA replacement built on 802.1x and
the Advanced Encryption Standard.
Really Simple Syndication - used for exchanging content between
websites. Often used to broadcast updates
ReSource reserVation Protocol - Used in VoIP. Enables the sender to
request a specific level of service across the network
Register transfer Level
Real-time Transport Protocol Used in VoIP to ensure that data is
reassembled in the correct order at the destination
Real Time Operating Systems
An interpreted scripting language for object orientated programming
Part of the Rails open source framework for developing database-backed web applications.
Although it is a pure object orientated language it can masquerade as a procedural one.
Created in Japan by Yukihiro Matsumoto and first released in 1995. It is written entirely in C.
-Run box history
Stored in
-Run time systems
Used for internal activation of system functions.
Run time software creates an environment in which an object program
can be run and debugged. Some run time systems are very similar to interpreters.
Scientific Advisory Committee
Super Audio CD. From Sony and Phillips. A one bit system with a
2.8224MHz sampling rate and a 100kHz audio bandwidth. Uses Direct Stream Digital (DSD)
instead of PCM. This approach records audio signals at a high sampling rate and then converts
them into 1bit digital data. The reproduction of an analogue waveform is extremely accurate. It
also eliminates aliasing filters and decimation digital filters in the recording studio as well as
interpolation digital filters in playback. SACD is a two channel product but multi-channel is
planned. Also see DVD-Audio
-Safe Mode
Hold down CTRL when W98 boots to get Start up menu. Then select
Safe Mode.
-Sale of Goods Act 1979
Goods must be fit for purpose and should be expected to last a reasonable life time
Speech Application Language Tags
An application used on Unix and Linux systems to enable SMB, so
allowing the Unix and Linux machines to appear on a Windows network so that file sharing can
take place.
Security Assertion Markup Language.
Storage Area Network. A collection of storage and networking
components that are dedicated and optimised to the task of attaching storage devices to servers in a
way that allows them to be shared. Fibre channel used for the high speed connection. The
command set protocol on a SAN is primarily Fibre Channel SCSI (FC-SCSI) as defined by the Fibre
Channel standard. The server sees a SAN-attached device as a directly attached SCSI device,
though the SAN could be anywhere on the dedicated fibre channel. A major implementation
difference between SANs and other networks is that the usual one to one correspondence between a
logical server and a physical box disappears.
Corporate governance regulations introduced by the US government.
It sets out the requirements for company auditing.
Serial Attached SCSI. Successor to parallel SCSI. Initial data rates
for SAS will be 3Gb/s and at least 300Mb/s.
Serial ATA. Speeds 150 - 300MB/s. Uses a cable with 7 wires. Uses
the data itself as the clock to avoid phase delays as found with Ultra ATA. Has a clock speed of
1500MHz, so giving a bandwidth of 150MB/s
object orientated programs.
The simple API for XML - a standard interface to XML parsers from
Use either CCDs (Charge Coupled Devices) or CIS (Contact Image
Sensor) technology. CCDs better and more common. The light source is usually a cold cathode
lamp (unlike a fluorescent tube it has no filament, generates little heat and provides a more
consistent white light).
Colour separation is achieved through a lens that splits the incoming light into three channels; red,
green and blue. These then pass through a colour filter onto a discrete section of the CCD. The
scanner combines all the data to form a single, full colour image.
The CCD records the lightness of the reflected or transmitted light as an intensity.
When the scanner scans an image, the lamp illuminates a thin strip of the image called a raster line.
The reflected or transmitted light is captured by the CCD array. In a 1200dpi scanner, where the
scanning width is 216mm (8.5"), there are 10,200 (8.5 x 1200) usable CCD elements in the array.
As the array is much smaller than 8.5", an optical system focuses the light from the raster line down
to the appropriate size of the CCD array.
scanner platter
white cold-cathode lamp
colour filter
and CCD
precision optics
scanning carriage
The smallest distance that the scanning carriage can move determines the vertical resolution.
CIS systems use a tightly packed array of red, green and blue LEDs. The optical system of a CCD
scanner are replaced with a single row of sensors mounted close to the source image. CIS scanners
can be much thinner than CCD scanners.
-SC connector
Used for optical fibre. Features a moulded body and a push-pull
locking system. To terminate a fibre, put strain relief sleeve onto fibre and then strip fibre to the
125µm coating using the Miller strippers. Check that the 250µm layer is removed by trying to
insert it into a connector! Inject a connector with glue from a syringe until excess comes through
the end of the connector. Wipe off the excess. Dip the stripped fibre into the accelerator and insert
into the connector (quickly!) and leave to set (30s). When set scribe fibre where it emerges from
connector with sapphire scribe (0.1mm). Break excess into the sharp box. Examine with
microscope to check that it is a clean cleave. Then start polishing with 12m film (grey?). Burnish
- ensure that the paper stays on the connector or it could damage the fibre. Then onto 5m film
(yellow), then finally 0.3m film (white) on base and using the terminator in the polishing puck on
the plastic surface. Use figure of eight motion. Wash with isopropyl alcohol. Examine with
microscope. Repeat until core crystal clear. Put on outer casing and push in using screwdriver from
the rear, taking care not to slip and break fibre. Push on strain relief boot.
System Configuration Editor. For W98 run msconfig.exe
In the context of Windows Server operating systems, a description of
the classes and their necessary attributes stored within Active Directory.
Serial Copy Management System. Used on Digital Audio tapes to
prevent copying.
Small Computer System Interface. Ultra3 SCSI introduces 160MB/s
data transfers through the use of double transition clocking (the data signals are clocked into the
receiver on the leading and trailing edge of the REQ or ACK signal. In Ultra2 SCSI, the REQ and
ACK clocks ran at 20MHz. In Ultra3 SCSI, both the data and clock lines now operate at 40MHz
50 pin
8-bit bus
50 pin
8-bit bus
68 pin
16-bit bus
Ultra SCSI
50 pin
16-bit bus
Ultra wide SCSI
68 pin
32-bit bus Also known as SCSI-3
Ultra 2 SCSI
68 pin.
Ultra 160 SCSI
160MBps. 16 bit bus but transfers data on both the rising and falling
edges of the clock signal
Hard drives are the only devices to use Ultra 2 SCSI.
Secure Digital memory cards - contain a manual write protection
Synchronous Digital Hierarchy. See SONET. Used in Europe
Single Document Interface. Used by Office 2000. See MDI
Synchronous Data Link Control. IBM standard protocol
System Definition Model - part of XML
Session Description Protocol - generally used with SIP to describe
the attributes of a SIP session. Although described as a protocol, it is more of a format for
describing multimedia sessions
Service Discovery Protocol. Used on Bluetooth
Software Defined Radio. SDR moves large parts of the analogue
circuits in radios into software which makes the radio programmable, and so can be easily updated
to cope with new types of signals.
Synchronous Dynamic Random Access Memory. A type of memory
that synchronises itself with the speed of the CPU bus. About twice as fast as EDO ram A number
starting with PC66 indicates 66MHz bus and PC100 indicates 100MHz bus. If individual memory
chips have -10 or -8 suffix usually indicates the operating time in ns. Uses a synchronous interface
with all inputs referenced to the rising edge of the clock allowing all of the address, control and data
input buffers to be identical.
DDR SDRAM data is driven relative to both edges of the clock, thus in effect doubling the data
speed of memory. PC266 (using a clock frequency of 133MHz), with the input and output data
changing every 3.75ns
Synchronous Digital Subscriber Line. Offers data rates of up to
3Mbps in both directions. SDSL is an umbrella term for a number of supplier specific
implementations over a single copper pair providing variable rates over a symmetrical service.
It uses 2B1Q HDSL run on a single pair with an Ethernet interface to the customer. It is likely that
this will move quickly towards the higher performance standard G.SHDSL.
-Search Engine
Used to find Internet sites. e.g.
Once a search engine knows about a site it will index it. This involves sending one or more
automated agents, or 'spiders' to work their way through the site following the links. To stop a
spider from indexing certain pages, create a file called ROBOTS.TXT and place it in the root
directory of the site. The format of the file is as follows:
User-agent: *
Disallow: /scripts/
Disallow: /news/
The first line specifies which search engines to exclude: an asterisk is a wildcard, meaning that all
search engines should obey the following rules, a list of directories that the engines should ignore.
Individual pages can be specified as in
Disallow: /backend/admin/logon.php
Comments can also be added by preceding them with a # character e.g.
Disallow: /news/ # No point in indexing these.
Search engines are only interested in text and not pictures. Meta tags are rarely used. Search
engines mainly interested in the main content and the title in particular.
Search engine and ranking rules - see
Single Edge Contact Cartridge. Used by Pentium II processors.
Fitted into a Slot 1 socket
Security Event Management
-Serial ATA
Replacement for parallel buses which suffer from cross talk, signal
ringing and cross talk. Needs only four wires to transfer data at 150MB/s as opposed to the parallel
ATA which transfers data at 133MB/s.
-Serial port
Serial Ports.
Null Modem Serial Cable.
9 pin to 9 pin. 2-3, 3-2, 5-5.
9 pin to 25 pin. 2-2, 3-3 and 7 (9 pin) to 5 (25 pin).
9 pin serial plug.
Looking at the base of a female plug.
5 4 3
2 1
25 pin serial plug
Pin 1
Data Carrier Detect DCD
Pin 8
Pin 2
Data in RXD
Pin 3
Pin 3
Data out TXD
Pin 2
Pin 4
Data terminal ready DTR
Pin 20
Pin 5
Pin 7
Pin 6
Data set ready DSR
Pin 6
Pin 7
Request to send RTS
Pin 4
Pin 8
Clear to send CTS
Pin 5
Pin 9
Ring Indicator
Pin 22
Data terminal Equipment (DTE) e.g. a microcomputer - fitted with a male connector.
Data terminating equipment (DCE) e.g. a MODEM - fitted with a female connector.
I/O lines usable on an RS232 port.
Some PC manufacturers use TTL levels instead of the +12/15V.
TXD can be used to gain a small amount of power for a control circuit. Set Break (bit 6, base + 3)
enables the TXD line to be made high permanently.
COM1 base address usually 2F8 and COM2 is usually 3F8
Elektor November 1996
edge RI
Serial port addresses and locations of I/O memory.
Transmit/Receive Buffer
Interrupt enable register
Interrupt identification register
Line control register(+3)
Modem control register
Line status register
Modem status register
Elektor March 2000
Secure Electronic Transaction. Developed by Mastercard and VISA.
Devised in 1996 but because proprietary software needed it has not made a big impact. Public key
technology is implemented to support authentication of all parties and encryption of all sensitive
transaction data.
System File Checker. Used to restore Windows 9X (not ME) from
Windows CAB files. W98 Start - Run - SFC
Shielded Foil Twisted Pair cables.
Standard Generalised Mark up Language. HTML is a simplified form
of this. Has been the defacto method of expressing data in text processing apps for high end
document publishers since 1986.
-Shadow Mask
Thin metal sheet of metal with thousands of tiny holes punched in it.
These holes are lined up with the corresponding screen pixels to ensure that the correct beam hits
the intended red, blue or green phosphors. Not as bright as Aperture Grille CRTs.
-Shannon Limit
The maximum amount that data can be compressed. Named after Dr
Claude Shannon the author of a 1948 treatise on communications technology. Worked for the Bell
labs during and after the war. Also invented the word Bit. Shannon's Law defines the theoretical
maximum rate at which error-free digits can be transmitted over a bandwidth limited channel in the
presence of noise. Usually expressed in the form C = Wlog2(1+S/N), where C is the channel
capacity in bits per second, W is the bandwidth in Hertz and S/N is the signal to noise ratio.(?).
Discovered that I = log2N where I is the number of bits of information in a message and N is the
number of different possible messages.
An object on WinNT that has been made available for network access.
Symmetric High bit rate DSL
-Shift *
inserting CD
Deletes an item without it going to the recycle bin.
Select to end of line
Repeats the last search, bypassing the dialog box.
Select to beginning of line
Select character to the right
Select character to the left
Bypass autoplay
-Short Code
First programming computer language - developed in 1949. Had to
be hand coded into binary until Grace Hopper, working for the US navy wrote the first compiler in
Microsoft scrap file format. Can hold anything.
A multi-vendor scripting language that provides a universal way for
users to create filters for e-mails.
Special Interest Group
Specific strings of binary code in most viruses (except polymorphic)
that allows anti-virus software to detect them.
Single Instruction Multiple Data. Also known as SSE
Single Inline Memory Module - small circuit boards which hold a row
of memory chips. 72 pin connector, and uses a 32 bit wide bus. As Pentium processors have a 64
bit bus, SIMMs must be installed in pairs.
SIP for Instant Messaging and Prescence Leveraging Extensions
Sessional Initiation Protocol. A protocol for initiating multimedia in
the application layer. Supports name mapping and redirection services, users can initiate and
receive communications from any location.
It works on a request/response basis, and participants are identified by URLs. Requests can be sent
through any transport protocol, such as UDP, SCTP, and TCP. SIP determines the end system to be
used for he session, the communication media and media parameters. Once confirmed, SIP
establishes call parameters at either end of the communication, and handles call transfer and
VoIP is poised to start replacing this network by running everything over the data network. The
potential cost savings make this a very attractive proposal, but there are still problems - the data
network was never designed to handle complex communications sessions.
In VoIP, none of the signalling protocols required are present, unlike in a PSTN system, and a user
may be constantly switching IP address, either by physically transferring his or her location or
because of the expiry of DHCP leases. This immediately makes it more complex to make
SIP is an IETF standard designed to provide advanced telephony services over the internet.
As the name suggests, it is used to establish, terminate and modify communications sessions in an
IP network. It began life as a component of the multicast backbone (Mbone) network. This was an
experimental network designed to deliver multimedia content over the network. SIP is not a
standalone protocol and doesn't actually understand what a session is. Instead it interoperates with
existing protocols and just swaps Meta data that enables session initialisation. A session can be as
simple as a two-way telephone call, but can also be a fully-blown multimedia conference call. As
SIP only provides the method for dealing with sessions, it has to work alongside other protocols and
standards, which provide the level of service required by real-time communication. Typically,
communications require a guaranteed delivery time, which can be provided by the real-time
transport protocol (RTP). Voice quality has to be guaranteed using protocols such as RSVP and
YESSIR. Directory integration with LDAP is essential for user discovery, while authentication
server support, such as RADIUS, ensures that users are correctly identified.
To facilitate proper communication, SIP has to provide a range of features and functions to
establish a session.
User Location. SIP has to provide the function that locates where a user is currently located. It is
common for a user to have a PC at work and home, a laptop and even a VoIP phone. An incoming
connection might require that all devices ring at the same time, that one device gets preference or
that a round-robin ring around takes place. SIP has to deal with this dynamic configuration
information and correctly locate the user.
Call Initialisation. Once a user has been located, a session has to be established. Although SIP
doesn't understand the session, it has to transmit the description of the session from the caller to the
receiver. This usually results in negotiation between all of the parties involved in the call. It could
be that a device doesn't support video, but only voice. SIP transfers this information using the
multipurpose internet mail extensions (MIME). This is used in web and email services to describe
content. This means there is always a wide-range of options available in negotiation. The most
common form of session description used by SIP is the Session Description Protocol (SDP).
Call modification. Once a call is established, SIP still has a role to play. A call in progress can
change features, such as a video stream being added to a voice conversation. New parties can also
be added into a conversation, which requires additional negotiation of features. Call modification
doesn't have to be as drastic as either of these measures. Common telephony functions, including
muting and call holding, are also supported by SIP. The range of call features supported depends on
the session description protocol in use.
Call TerminationAfter. When all users are finished with the session they hang-up. SIP has to deal
with this call termination.
Client/server architecture of SIP.
The User Agent Client (UAC) sits on the client and is responsible for making any SIP requests to
other clients. The UAC is also the component that accepts and deals with any request that comes in,
including call initialisation, modification and termination.
User Agent Server. There are three types of user agent server (UAS): stateful proxy server, stateless
proxy server and the re-direct server. Proxy servers receive request and work out where to send
them. This is generally onto the next server until the destination is located. A stateful proxy server
retains information of all requests and responses. This can be used to send a request to multiple
destinations and only pass on the best response. A stateless proxy server simply passes requests on
but doesn't retain any information.
A re-direct server doesn't proxy requests, but returns the destination address to the caller. The caller
can then make a request directly to the destination.
To see how this works consider a simple example of user 'A' trying to call user 'B'. A's UAC
sends a SIP invite request to its local UAS. If this is a proxy server, then it forwards the request to
the next UAS until it hits its destination. If it is a re-direct server then it returns the direct address of
B. In SIP, addresses are represented as URLs and follow a similar layout to email addresses.
The invite includes a full description of the session including all of the media streams that A wants
to use. B replies to the invitation, but includes a description of any modifications that he wants to
make. This is for compatibility reasons, as B might support all of the features that A asked for.
After this negotiation is completed, the session is created and A and B can communicate. At the
end of the call, either side can send a disconnect, terminating the session.
All of this process is automatic. For example, when A calls B, if B picks up his VoIP videophone,
the phone automatically handles the media negotiation process. When B puts the phone down, the
disconnect is automatically sent. It is also the job of a SIP device to register its current location with
a UAS. This ensures that a user can be found even when mobile.
In the simple example above, only a single connection was covered. However, SIP can use a
process called 'forking', which sends out invites to multiple devices at once. The first device to
respond gets the connection. This is similar in conception to a phone pool in a helpdesk, where all
incoming calls ring all available phones. However, this feature is only available if a stateful proxy
server is used, as it needs to remember which connections to allow and which to block.
SIP can return different media types. If a client connects to a company, then they could return a list
of phone numbers for the building. It means that information can be dynamically created and
SIP has well-defined messages that are used for communication. A message can either be a
request or a response message.
INVITE is used to initiate a call and is also used to change call parameters once a session has been
established. This can be thought of as a re-INVITE.
ACK is an acknowledgement and confirms response to an invite.
BYE terminates a call in progress.
CANCEL Terminates the invite and stops all searches and devices that are ringing.
OPTIONS Used to query the capabilities of a device.
REGISTER Registers a device's location with a server.
INFO Sends information during a session but does not modify the session state.
Response messages contain numerical responses and are similar to those used by HTTP:
1xx provisional, searching, ringing, queuing
2xx success
3xx redirection, forwarding
4xx request failure (client)
5xx server failures
6xx global failure (busy, refusal, not available anywhere.
100 Continue
180 Ringing
200 OK
301 Moved permanently
302 Moved temporarily
400 Bad request
408 Request time-out
480 Unavailable
600 Busy
603 Decline
604 Does not exist
SIP Message architecture. Both request and response SIP messages are built from the same
three components:
Start Lines. The Start Line is the beginning of every SIP message. It is first used to identify the
type of message and the protocol. Depending on the message type the Start Line is either a Requestline for requests or a Status-line for responses.
A Request-line includes a Request URL, which is used to identify the requested user. This line can
be rewritten by proxies, although the 'To' field later on cannot.
A Status-line holds the numeric Status-code and the text version.
SIP headers contain a list of fields that are used to identify message attributes. The syntax
The body conveys the mechanics of a connection. It is common for the body to hold
protocol information such as SDP, and only the receiving client can understand what the body
visualisation effects that customise the appearance of programs. e.g.
Media Player, Winamp etc.
Service Level Agreement. Defines the level of network services
provision expected.
Serial Line Interface Protocol/Point to Point Protocol. These are both
standards for connecting directly to the Internet, as opposed to having to log on to it via a host
-Slot 1
Used by Pentium II and early PIIIs
-Slot A
AMD Athalon slot socket. Same size as Slot 1 but the processor
fitted in the other way round
Scalable Linear Recording. Tandberg format for back-up tapes. It is
a revised version of the quarter inch tape (QIC) format and currently stores 25GB per cartridge with
a data transfer rate of 2MB/s. Cheaper than DLT and has a mean time between failure of 300,000
Source Level Routing - an IP routing technique that allows the
originator of an IP datagram to specify the precise route that delivery should take.
Shared Memory Architecture
Self Monitoring, Analysis and Reporting Technology. A series of
diagnostics built into a hard drive that continually checks to make sure the drive is functioning
correctly. By monitoring the drive it is possible to pick up on any fatal data errors before they
-Smart Media
Memory card. Contains no on board memory.
Server Message Block - used by Windows servers. Also referred to as
CIFS (Common Internet File System). The protocol is used to allow applications to read and write
files or request services from remote machines. Developed by Microsoft and runs on top of other
network protocols such as TCP/IP, IPX or NetBeui. SMB is the protocol used for network file
sharing in Windows and DOS. NetBios protocol is based on SMB.
Small, Medium Enterprise
Synchronised Multimedia Integration Language. Part of XML.
Provides a platform for Web based multimedia applications. First introduced in 1998
Service Modelling Language - defines the way IT resources are
described in XML
Symmetric multiprocessing. Uses a second processor when the first is
Short Message Service.
System Management Server (Microsoft)
Simple Mail Transfer Protocol. The Internet standard for mail
delivery. The TCP/IP protocol for electronic mail.
Uses TCP port 25.
Has limited queuing facilities and so is used with POP3 or IMAP4 servers for client message
Uses plain text messages to transmit the data
Telnet to an e-mail server and type HELP - should give a list of commands.
Can be used to fake e-mail addresses by typing the wrong e-mail address into the 'FROM' field.
When an e-mail address is scanned e.g. user@domain, the sending station drops the user
component and uses a DNS server to look up the mail record part of the domain name. The
transmitter then opens an SMTP connection to the mail server and transmits the e-mail.
Simple Network Management Protocol.
Simple Network Time Protocol
Service Orientated Architecture - a way of organising data and
applications that enables output to be delivered in services that are meaningful to business. This
requires the description of the business function to be separated from the content and process. By
wrapping data and process in a layer, and publishing it as a service in a standard format, a service
can be called up on demand by other services.
Simple Object Access Protocol. Closely related to XML, this is a
protocol specification for invoking methods in servers, services, components and objects.
Underpins MS .NET
Alternative name for Port on an IP network
-Socket 7
Used by Pentium, Cyrix 6x86, MMX, 6x86MX and K6. Usually ZIF.
-Socket 8
Used by Pentium Pro
-Socket 370
370 pins. Modern ones accept either Celeron or PIII processors.
Accepts processors in the PPGA format
Small Office, Home Office.
Synchronous Optical Network. Known in Europe as SDH. This is a
standard from the 1980s for metropolitan fibre rings used in ILECs. Traffic is carried in an
electronic packet transported over fibre, using dual counter-rotating rings. The systems are
relatively inexpensive to implement, but they were designed in the 1970s for primarily circuit
switched voice traffic so they make very inefficient use of bandwidth in carrying traffic that is
mostly IP-encapsulated data.
-Sound Cards.
8-bit samples give about 48dB of dynamic range while 16 bit gives about 96dB.
Wavetable synthesis: the sounds of genuine instruments have been recorded and digitised. Uses very
short samples.
FM synthesis: the sound of instruments are simulated based on a mathematical algorithm rather than
actual recorded sounds.
Developed over 20 years ago, creates sounds by modulating a simple pure tone carrier wave with a
second waveform. This produces a third complex waveform from which it is possible to produce
instrument type sounds. The most common synth chip is the Yamaha OPL-3, gives 20 simultaneous
stereo voices.
You can create a WAV file in Sound Recorder. To produce from a CD, put CD in drive and select
Start, Programs, Accessories, Multimedia, Sound Recorder. Once the program is up, start playing
the CD. To adjust the sound, select Start, Settings, Control Panel, and double click the multimedia
option. The Audio tab contains options for altering the recording.
Settings and functions.
01 and 05
0220 - 022F
0330 - 0331
0388 - 038B
0224 mixer register
0225 mixer data
0226 dsp reset port
022A dsp read port
022C dsp write port (command/data), dsp write-buffer status (bit 7)
022D (dsp timer interrupt clear)
022E dsp read-buffer status (bit 7), dsp interrupt acknowledge (8-bit?)
022F dsp 16-bit interrupt acknowledge
-Source code
The original code written in either a high level or a low level
Absence of signal, in telegraph communciations, a space represents
the open condition or no current flowing. A "0"
Serial presence Detect. - Memory timings.
Service Profile Identifier. A number that identifies terminal
equipment attached to an ISDN line.
Spam Over Internet Telephony
Smart Personal Objects Technology. - Backed by Microsoft.
Programsinstalled by advertising companies on your computer when
you use the Internet. Includes:- VX2/a, SurfPlayer, DownloadPlus 1.0.6, Search-Explorer,
Weathercast, FileFreedom, FirstLook, ezCyberSearch, Mass Instant Messenger 1.7, OnFlow,
First U.S. mobile operator to launch 3G service
Structured Query Language. A standard language for talking to
Storage Resource Management
Secure Shell - an internet encryption system
Shared source Initiative
Service Set Identifier - a 32 character unique identifier attached to the
header of packets sent over a wireless LAN. Sent as unencrypted text and is vulnerable to being
sniffed by third parties.
Spanning Tree Algorithm (IEEE802.1D) designed to prevent
flooding in bridged networks.
Steplocking is a technology used in high-availability servers, where
each CPU runs the same task, ensuring that each one has carried out the function and that the
outcome is the same. If there are differences, the system sees which of the CPUs is right, and the
'faulty' CPU is either disregarded or taken offline, with the remaining CPUs taking over. Every
'step' taken is 'locked' into place once checked. State is always maintained and high availability is
provided. The more CPUs there are the better the steplocking.
Spanning Tree Protocol. See above.
Secure Sockets Layer. Developed by Netscape and has become the
internet standard protocol for providing a secure communications channel for session based
encryption and authentication. Supported by all of the popular netbrowsers. The protocol runs on
port 443. An SSL handshake involves the server responding to a client request by sending its digital
certificate and cypher preferences. The client generates a master key, encrypts it with the server
public key and transmits the encrypted master key back to the server. The server recovers the
master key, returns a message authenticated with it to the client by way of authenticating itself and
then all subsequent data exchange is encrypted and authenticated with keys derived from the master.
SSL is application independent and can operate with http, ftp, or telnet. SSL based systems do not
identify client to server unless this is specified as an option and even then only when certificates are
distributed to all users. At the end of the session the keys are disposed of.
A network topology where the central control point is connected
individually to all stations.
-Stateful Inspection
A type of firewall engine that works in the network layer. More
secure that packet filtering firewalls which just check the header of the incoming packet. Stateful
Inspection engines can look inside packets up to the Application layer.
-ST connector
Used for optical fibre. Uses a bayonet locking system. Has a ceramic
-Stealth Virus
Uses tricks to conceal itself from anti-virus software. Mainly affect
DOS not windows applications
Greek words meaning Covered Writing. Hiding messages as in
pictures and digitally watermarking media to avoid copyright theft.
Hides one piece of information in the background noise of another, e.g. a word document inside a
Jpeg file.
Shielded Twisted Pair cable.
Spanning Tree Protocol.
Sequential Transfer Rate. The speed at which a hard disk can read
data from sequential tracks and cylinders on the platters.
This is when the printer misaligns the lines of print, leaving out a
small amount of the page, which shows through as a thin white line.
-Structured wiring
A term applied to a cabling system implemented within a building as
a pre-planned utility.
(Also see IP addresses). Allow a network class to be split up for
internal use only. To the outside world they still look like a normal network. The subnet part of the
address is used to define how many bits to use as the network address and how many to use for the
host address. An example of a class C network is shown below.
Network Address
11111111 11111111 11111111
The subnet address means that we can have four subnets 00, 01, 10, 11. This is using classless
inter-domain routing (CIDR) subnetting. In classic subnetting, 0 and 1 are reserved, which reduces
the number of available subnets and also host addresses. In this example, the six bit host address
means that each subnet can have 62 hosts on it. The important part of this is the subnet mask,
which allows us to determine the subnet a host belongs to. Only hosts on the same subnet can talk
directly to each other.
Subnet masks are also 32 bit numbers that follow the IP dotted -quad notation. To work out which
bits are 1s and which are 0s:- all bits in the network address portion are 1s, followed by making all
the bits in the subnet mask 1s, while all the bits in the host address are 0s. So for the class C
example the subnet mask is 11111111 11111111 11111111 11000000 which gives
To see how this is used take two IP addresses and To see if they sit
on the same network we perform a Boolean AND on each address with the subnet mask.
So AND equals also AND equals
Since both calculations give the same network address, we know that the hosts are on
the same subnet and are allowed to talk. If the second IP address was an AND
with would give Since this differs from the the
addresses must reside on different subnets.
The subnet mask will differ depending on the class of the network, but class C networks will always
have a subnet mask that starts 255.255.255 A subnet mask of255.255.255.0 means that all hosts
on the network can talk to each other.
Other valid subnet masks on a class C network are given below.
Subnet mask
Number of subnets
Hosts on each subnet
In the example the range of addresses would be:
Range of addresses - 62 - 126 - 190 - 254
The missing addresses are used for the network address and the broadcast address. So the first
subnet has a network address of 192.1168.72.0 and a broadcast address of while
the last has a network address of and a broadcast address of
For subnetting to work, routers have to be updated, adding entries of the type (this-network,
subnet,0) and (this-network, this-subnet, host). This allows a router to route between subnets.
Start of Text. A control character used to indicate the beginning of a
message. It immediately follows the header in transmission blocks.
-Summer Time
In the UK the clocks go back at 3am on the last Sunday in October
and go forward at 2am on the last Sunday in March.
Software Update Services - Microsoft. Provides the latest patches.
Super Video CD. Supported by lots of DVD players. Developed in
China as a follow on from VCD (video CD). It is not as high quality as DVD video but is better
than VCD
Structured Vector Graphics - XML based language for displaying
vector graphics. Scalable Vector Graphics.
Shared Wireless Access Protocol
-Swap file
Also known as virtual memory, this is a portion of the hard disk set
aside for Windows to use as a cache, basically to speed up transfers to and from disk.
format. Used in Flash
Shockwave for Flash file format a web optimised, vector based
An intelligent hub that reads the destination addresses of incoming
data packets and only sends them to the port where the recipient is physically attached.
Switches used to form VLANs. Can support two kinds of VLAN membership - Port or MAC
Layer 3 switches have routing capabilities and so can be used for the core of a VLAN network. As
packets arrive, the switch can make the decision on whether to route or switch a packet.
The process by which data packets are received, stored and
transmitted to the appropriate destination port.
A relational Database Management system. Invented at the university
of California Berkeley. A deal with Microsoft led to Sybase code being used for SQL server. When
the deal broke up, Sybase SQL Server was renamed Adaptive Server and Microsoft re-engineered
and re-wrote the code.
A consortium of companies (Psion, Phillips, Nokia, Matsushita) that
has developed the EPOC operating system for mobile devices including phones.
-Synchronous transmission
Data bits are sent at a fixed rate with the transmitter and receiver exactly in time. Eliminates the
need for start and stop bits.
The XML based data synchronisation protocol.
PC interface system for peripheral devices.
System Editor. Used to edit system files in W9X (not ME). In ME
use Msconfig.
-System File Checker
The data base for this is default.sfc
The windows equivalent of the config.sys file.
Contain the hardware details. To comment out a line place a colon at the beginning of the line.
Telephony Application Program Interface
Target channel Adapter, an adapter that connects an InfiniBand link to
an I/O device such as a disc subsystem
See Digital Telephony
Trusted Computing Platform Alliance
Total Cost of Ownership
Standards for monitors. Minimum refresh rate for monitors should be
A Health and Safety standard for monitors.
Trusted Computing Platform Alliance. Founded in 1999 by HP,
Compaq, Intel, IBM and Microsoft. The goal is to employ various checks in software and hardware
to detect and then enforce the conditions under which particular bits of data and code can be used.
Microsoft Palladium project
Transmission Control Protocol / Internet Protocol originally
developed by the US Department of Defense in the 1960s during the cold war. The DoD's Arpa
(Advanced Research Projects Agency), now called Darpa, began a partnership with US universities
and corporate researchers to design open, standard protocols and build multivendor networks. The
fruit of their work was ArpaNet, the first packet switching network running the NCP (Network
Control Protocol). In 1974, Vint Cerf and Robert Kahn proposed a new set of core protocols for the
ArpaNet, which developed into TCP.
TCP/IP is the protocol used by the Internet and many intranets and LANs. Each device is given a
unique address in the format Each of the millions of computers on the Internet
must have a unique TCP/IP address in order to be correctly identified. Used to send packets across
multiple networks.
TCP/IP has its own reference model, which differs from the OSI reference model.
It is actually two protocols - Transmission Control protocol (TCP) and Internet Protocol (IP). IP is a
connectionless protocol and unreliable, while TCP is connection-orientated through a three way
TCP runs over the top of IP, which runs over the top of the network protocol it is on. IP was
designed to let hosts inject packets independently into the network and have them routed to their
destination. Packets can even arrive in different orders. This is known as the internet layer in the
reference model.
The need for routing, and avoiding congestion, means the internet layer is very similar to the
network layer in the OSI model. Layers 1 and 2 are replaced by the host-to-network layer, which
lets IP packets drop onto heterogeneous networks.
Above this is the transport layer, which allows two stations to communicate. It provides the same
function as the transport layer in the OSI model. It defines two end-to-end protocols, TCP and UDP
(User Datagram Protocol). TCP introduces flow control and provides reliable transmission. UDP is
a connectionless, unreliable protocol for applications that don't need TCP-level reliability. UDP is
often used where prompt delivery is more important than error checking, as is the case with
streaming voice and video. The TCP/IP model jumps straight to the application layer. It contains
all of the higher-level protocols and includes Telnet, FTP, SMTP, DNS, NNTP and HTTP.
Time Division Duplex - only supports data not voice.
Time Division Multiplexing. Transmitting multiple channels on a
single transmission line by connecting terminals, one at a time, at regular intervals.
Time Domain Reflectometry. Used to determine cable length.
-Telecommunications (Lawful Business Practice) (Interception of Communications)
Regulations 2000
The Lawful Business Practice regulations supporting the Regulation of Investigatory Powers Act set
out the purposes for which monitoring may be used. These include ensuring compliance with
acceptable use policies and other organisational rules, but only after users have been informed of the
rules in advance.
-Telephone numbers
pay as you go
needed when caller line ID is suppressed on your telephone.
free anytime numbers.
BT clear line
A terminal emulation program used for logging onto another
computer, especially a large mainframe such as those containing the online catalogues of libraries.
Trans-European Network at 155Mb/s. A project to connect European
Academic and Research networks at 155Mb/s.
-Ternary DRAM
Three states 0, 1, don't care
Thin Film Transistor. A high quality liquid crystal display screen that
uses between one and four transistors per pixel to control illumination. Each transistor requires
little power and has a fast response time, so it can switch on and off very quickly.
Three main types. The oldest - TN+film has relative poor viewing angles around 115° and a slow
response time.
IPS - In Plane Switching - improves the viewing angle to around 160°. A slightly different method
is used by MVA - Multidomain Vertical Alignment - panels, where each pixel is given four areas.
These areas adjust their intensity to even out the brightness when viewed from different angles.
These also have viewing angles of around 160° and a faster response time.
The best are the Super-IPS panels and have a viewing angle of up to 170° and an even faster
-Thick Ethernet
See 10BASE5.
-Thin Ethernet
See 10BASE2.
Telecommunications Industries Association (of North America).
Tagged Image File Format. Used to store bit mapped images.
-Tight buffer fibre
outer jacket
aramid yarn
optical fibres
Four core fibres have colours of blue, orange, green and brown.
Eight core fibres have colours of blue, orange, green, brown, grey, white red and black.
Infra red radiation used at a wavelength of 850nm.
Attenuation losses for 62.5/125 fibre at 1Gbps are 3dB/km, 0.7dB/connector and 1.5dB/connector
pair, 0.3dB for a fusion splice.
Maximum length for 62.5/125 fibre at 1Gbps is 220m. For 50/125 fibre at 1Gbps is 550m.
See SC connector for termination.
-Tim Berners-Lee
Credited with inventing the World Wide Web in 1989 and wrote the
first Web client and server in 1990. He is a director at the W3C, the open forum for Internet
technology development. He holds the 3Com founders chair at the Laboratory for Computer
Science at the Massachusetts Institute of Technology (MIT).
Tablet PC Input Panel
-Tiresias Screen Font
Font designed to avoid legibility problems. Initially devised for
Temporal Key Integrity Protocol. Improvement upon WEP and uses a
128-bit temporal key combined with the client's MAC address
Top Level Domains
Transport Layer Security - a protocol that ensures privacy between
communicating applications and their users over WLANs and the internet.
-Token Ring
A type of network where all of the computers are arranged
(schematically) in a circle. A special bit pattern travels around the circle. To send a message, a
computer catches the token, attaches a message to it, and then lets it continue to travel around the
network. The traditional data transfer rate for token ring is 16Mbps though if duplex network cards
are used this can be increased to 32Mbps.
The physical layout of a network. See Network Topology.
Type of Service - also known as IP Precedence - is information
defined in two fields of the IP header. The first field, precedence, is used to identify and route
packets. A second field, the ToS sub-field, can define the type of service requested for the traffic.
Used in VoIP.
Transmit Power control - enables WLAN clients to use the minimum
output power necessary to transmit data signals if interference with other transmissions is
encountered. See IEEE 802.11h
Trusted Platform Module
(And retraining) The process by which modems negotiate their
communication speed depending upon the amount of noise on the line.
A LAN topology that recognises only one route between two nodes on
a network. The map resembles a tree or the letter T.
A program that looks legitimate, but performs some illicit activity
when it is run.
Terminate and Stay Resident. A program designed to remain easily
accessible even while another application is running. It can stop running but stay in the PCs RAM.
Transfer of Undertakings (Protection of Employment). Designed to
protect employees' jobs, pay and conditions, when organisations sold or outsourced parts of their
business operations to other companies or contracting firms.
AMD Athalon 64 second generation notebook cpu
Technology Without An Interesting Name. Software driver that lets
peripherals such as scanners and digital cameras be controlled from the PC and transfer their data to
-Twisted Pair Cable
The most common form of communications cabling used by
telephones, computer terminals and LANs.
The User Agent Client - a SIP component that sits in end-user devices
such as IP handsets or software applications to initiate and answer IP calls
The Universal Asynchronous Receiver/transmitter chip controls the
transfer of data over a serial port. Modern chips include 16550 or even better 16650. Older types
include 8550.
The User Agent Server sits in the network device such as PBX or
media gateway and handles SIP call signalling
Universal Description, Discovery and Integration. Provides a
directory of Web services, which can be used to search for companies involved in Web services, or
to file and find pieces of code that have been created for Web services, and which can be reused by
the same or by other organisations.
Ultra DMA. The latest types of EIDE controllers that support data
rates of 33MBps, 66MBps, 100MBps and 133MBps. Hence UDMA66 etc.
Two different devices are supported on each UDMA channel and most mother boards have two
such channels.
UDMA66 is only possible if an 80 wire cable is used and if all devices support UDMA66 on the
same interface. Otherwise it runs at the speed of the slowest interface.
User Datagram Protocol
Uniform Domain Name Dispute Resolution Policy
The United Kingdom Education and Research Networking
University of London Computing Centre.
-Ultra ATA
An IDE interface that transfers data at up to 133MB/s. Needs an 80
wire cable with a maximum length of 18 inches for reliable operation. The clock signal is sent with
the data but this leads to phase distortion of the clock signal and so speed limitations.
-Ultra SCSI
A SCSI standard that transfers data at 20MB/s.
-Ultra II SCSI
The latest SCSI standard that transfers data at 80MB/s.
Unified Modelling language, the standardised language for software
blue prints.
Universal Mobile Telephone Service
-Uninstall Programs.
Ensure nothing runs on Start Up: - Start - Run - msconfig - Enter - Startup Tab - Uncheck programs.
Remove file association: - Windows Explorer - Remove association.
Registry: HKEY_CLASSES_R¥\Applications. Click + then right click subkey matching program's file name.
Select and delete.
HKEY_CURRENT_USER\Software Find subkey of program's vendor - delete
HKEY_LOCAL_MACHINE\Software key - search and delete registry for any reference
Delete Program folder and shortcut.
Unified Incident Reporting and Alert Scheme. Founded in 1992.
Role to gather information on software problems. Now part of NISCC. The UK governments
CERT (Computer Emergency Response Team).
An operating system developed by AT&T Bell laboratories and used
on many backbone Internet servers. Developed from Multics, a bloated, ambitious OS that ran over
time and budget in the late 50s. When the plug was pulled, two engineers, Ken Thompson and
Dennis Ritchie, devised their own OS, originally known as Unics. Unix is a powerful multitasking
OS originally written in 11,000 lines of code (compared to 5.6 million for NT4 and an estimated 29
million for Windows 2000). Originally Bell distributed Unix at low cost and with the source code,
which was therefore customisable. By 1982, with US government restrictions lifted and Bell sold
off, AT&T decided to capitalise on the success of Unix and charge much money for it. Richard
Stallman, who worked at MIT, set up the Free Software Foundation in 1984. During the 1980s
Stallman and a group of Hackers set about creating GNU and created many programs but not the
kernel - later done by Linus Torvalds
-Upper Memory Area
The RAM between 640KB and 1024KB
Uninterruptible Power Supply. A device that provides battery backup
when the electrical power fails or drops to an unacceptable voltage level. Can be set to alert
computers to shut down in an orderly manner when a power outage has occurred and the batteries
are running out.
Also provide surge suppression and may provide some voltage regulation.
Standby UPS - "offline" until the mains supply fails then switches on within a few milliseconds
Line interactive UPS - smooths out the mains waveform and corrects the rise and fall of the voltage.
Online UPS - the inverter is continuously providing clean power from the battery and the computer
equipment is never receiving power directly from the mains
Unique Resource Locator. The address of a page on the Web. e.g.
the URL tells the browser to use HTTP protocol to find the server
named and ask it for the page entitled cricket.htm, which is found in the sport
directory. Usually consists of four parts: protocol, server (or domain), path and file name.
eg.http/ magazine/tips/ default.htm
Universal Serial Bus. A host-slave system Transfer rate of 1.5Mbps.
(Normal serial bus max speed of 115Kbps.) Originally conceived by Intel, Microsoft, Digital,
Compaq, NEC and IBM. Can be hot swapped, the relevant driver being automatically loaded. Plug
and Play, supports up to 127 devices with speeds of 12Mbps. Hot swappable.
Type A sockets (flat) on PC or hub side. Will provide up to 500mA.
Hubs can be nested up to 5 deep.
View from bottom of socket (PCB side)
Type A
Type B
Type B sockets (square) on peripheral which logs onto PC. Draws power.
USB cables always wired 1:1
Speeds of up to 12Mbps
Speeds of up to 480Mbps
USB On The Go. USB Standard, Rev 2.0. Allows for mobile
interconnectivity, by allowing a USB peripheral to be more than a simple peripheral. ie a DRD Dual Role Device.
One of the windows kernel files
Unstructured Supplementary Service Data. (Mobile phones) Often
referred to chat services. Faster than SMS. SMS uses store-and-forward functionality, USSD is
session orientated. When a user accesses a USSD service, a session is established and the radio
connection stays open until the user, application or time-out releases it. During a call, USSD uses
the FACCH (Fast Associated Control Channel) which is five times faster than the SACCH (Slow
Associated Control Channel) used by SMS.
Unshielded Twisted Pair cable.
Unix Copy Program - Early Internet Mail System
Ultra Wideband. Promises speeds of up to 1Gb/s by transmitting data
over a wide spectrum of frequency bands and at low power levels. Range <10m.
UWB is defined as any radio technology having a spectrum that occupies a bandwidth greater than
20% of the centre frequency, or a bandwidth of at least 500MHz
Synchronous/asynchronous data transmission, full duplex operation
over 2-wire leased or dialup lines; 1200bps data rate (V.22.bis, 2400 and 1200 bps).
-V.25, V.25 bis
Provides for automatic calling and answering circuitry for use on
dialup lines. V.25 parallel interface, V25 bis serial interface.
Synchronous/asynchronous data transmission, full duplex operation
over 2-wire dialup lines; 9600bps. Trellis encoding modulation used to minimise errors.
-V.32 bis
Synchronous/asynchronous data transmission, full duplex operation
over 2-wire dialup lines; supports data rates of 14400, 12000, 9600, 7200, 4800 bps data rates. Use
training and retraining to determine the speed of transmission depending upon the amount of line
Synchronous data transmission, full duplex over four wires. Uses the
same signal modulation techniques as V.32 modems.
Synchronous/asynchronous data transmission, full duplex operation
over 2-wire dialup lines; supports speeds up to 28.8kbps
CCITT (ITU) standard governing data transmission at 48Kbps over
60-to 108kHz group band circuits.
-V.42, V.42 bis
Uses two algorithms for error control and data compression. Uses
MNP 1-4 and LAPM to control data errors and retransmit 'bad' data blocks Can usually provide
data compression at 4:1.
Error compression system for modems.
Standard for modems giving 56Kbps.
Virtual Disk Storage - MS Windows 2003
Visual Display Terminal. Useful BSI publications
BS7179 Ergonomics of design and use of VDTs in offices
BS EN 29241 Code of practice for design of VDT work environments
Visual Display Unit. See VDT
Video Equipment Standards Association. Responsible for the VESA
Local Bus (VL-Bus)
-Video connector
Type VGA analogue, 15-way DIN in 9-way shell, 3-row D-type
Display adapters.
MDA, monochrome display adapter. Each character was displayed on a 9x14 grid, giving 80
characters per line and 25 lines to the screen.
CGA, colour graphics adapter. Four colour display and 8x8 grid giving a maximum resolution of
320x200 pixels.
EGA, enhanced graphics adapter. Could display monochrome text in a 14x9 matrix at resolutions
of 720x350 but also CGA colours at 320x200.
VGA, versatile graphics adapter. 640x480 with 16 colours.
SVGA 800x600 at 256 colours or even higher resolution.
XGA 1200x1024
256 colours
65536 colours
16,700,000 colours
Red (O)
Green (O)
Blue (O)
Not used
Digital ground
Red ground
Green ground
Blue ground
Not used
Digital ground
Not used
Not used
Horizontal sync (O)
Vertical sync (O)
-Video memory
-Virtual Machine (VM) An operating system running inside an operating system. Several
virtual machines can run inside a host operating system, with each behaving as if it were running
independently on its own physical hardware. All requests for hardware access are routed through
the host operating system.
Gives main frame type advantages to open systems storage
infrastructure. Enables companies to replace dedicated i/o controllers with software solutions
running on commodity hardware. Two types of virtualisation - in-band and asymmetric. In band
software is like a receptionist - handling calls to the SAN, while asymmetric systems force you to
make calls directly to extensions within the SAN but provide you with a phone directory to do so.
In a virtualised system, a layer of middleware is introduced between the systems administrator and
the disparate resources that make up the infrastructure: the administrator gives instructions to the
middleware asking it for specific resources as and when the need arises. The middleware deals with
the necessary devices, reallocating storage space, CPU power and other necessary elements under
the covers.
Virtualisation systems used on non-mainframe systems can be split into those dealing with storage,
processing power and network resources.
Virtualisation enables a system's physical resources to be shared by different tasks and so it helps
achieve higher utilisation of the assets.
First PC virus, Pakistani Brain, appeared in 1986. Amjad and Basit Farooq Alvi. Used by the
brothers to punish users of illegal copies of their software.
Jerusalem uses Interrupt 21h.
Michelangelo is a boot sector virus - on March 6th it wipes both hard and floppy drives as soon as
the PC is turned on.
Starship only infects files when they are copied from hard disk to floppy. It also creates a new boot
partition on the hard disk to store the virus code then runs the real boot sector stored in the original
Polymorphic viruses are capable of changing form.
Anti-CMOS virus:- clears the hard disk number and changes the floppy drive to 5.25in, 1.2Mb.
AWARD_SW, Biostar, Biosstar, Award*: try upper and lower characters.
Types of virus scanners.
"Checksum" generate a checksum or CRC for every executable program each time the scanner is
run. It then checks for changes between scans to detect viruses.
Programming languages that allow all coding to be done graphically.
Visual C++ an object orientated language with advanced template features, low level platform
access and an optimising compiler.
Visual Basic Roots in Microsoft original version of Basic. Object orientated additions.
Visual C#
Microsofts competitor for Java. Aimed at distributed Web services applications.
Formally called ASP+. ASP.NET is a successor to Active Server Pages
(ASP). Started life as extensions to HTML. ASP.NET can produce compiled code and incorporate
applications written in any of the other .NET languages.
An interpreted, object-based scripting language that has fewer capabilities than C++.
Related to Javascript. JScript is limited by its inability to read or write files and cannot be used to
write standalone applications. Scripts can only run under an interpreter or host, e.g. ASP, IE, etc.
Win95.cih on 26th of April or sometimes any month it attempts to
overwrite all of the data on the hard disk. For machines with a Flash BIOS it also attempts to
overwrite that and so render the motherboard useless.
Volume License Agreement
Virtual LAN. Standard IEEE802.1q VLANs let you segment
network services according to users' business rather than physical location. Implemented using
switches. There are two kinds of VLAN membership - Port and MAC address. Most VLANs are
based on port membership - each port is given a VLAN ID - which is just a number. Switches are
initially shipped with all ports having the same VLAN ID.
All ports with the same ID are in the same VLAN. When a packet comes into the switch, the switch
will only pass that packet onto a port with the same VLAN ID number.
VLAN tags - added to Ethernet packets between VLAN switches - an extra 4 byte field. The
receiving field has to strip this away before passing on the packet.
VESA Local Bus. Developed by Video Electronics Standards
Association. Replaced by ISA bus and PCI.
Very Long Instruction Word
Voice Over Internet Protocol.
VoIP is the process of sending digitised speech across an IP network. Although it refers to any
speech transmitted in this way, the most common application for VoIP is IP telephony. To mirror
the quality and efficiency of a circuit-switched telephone network, there are an array of processes
that VoIP has to address. These include call setup and termination, compression and encoding,
transportation, and management of bandwidth. Underpinning all of these is the design of the
network used to transmit VoIP traffic and provide QoS.
To begin a VoIP session, a call has to be set up between two end points, simulating the
process of connecting and disconnecting two telephone handsets. This process uses one of two
major protocols - H.323 or Session Initiation Protocol (SIP), both of which work at the Application
Layer-7 of the OSI 7-layer model. There is some debate about which of these will become
dominant in future VoIP strategies, although H.323 remains the more established technology. The
two protocols can co-exist, however.
H.323 is made up of lower-level protocols that manage digital voice transmission. These protocols
include signalling, security, controls for transferring data between domains, call initiation and
termination. As a result, any hardware conforming to the standard is interoperable. But, H.323's
breadth is also its weakness. Inflexibility and poor scalability cause implementation problems.
SIP is a newer, more flexible text-based protocol. It describes data being transmitted using MIME
or XML, and generates a connection between two end points. SIP relies on other protocols to
handle encoding, data compression and data management.
Users are identified by Uniform Resource Identifiers (URIs) which allow a call to be
connected by clicking on a web link, or typing in an address similar to an email. Beyond VoIP, this
approach opens up possibilities for linking voice to other services, such as instant messaging and
email. However, this requires a phone with a suitable keyboard for typing URIs.
SDP The Session Description Protocol is generally used in conjunction with SIP to describe the
attributes of a SIP session. Its parameters are included in the message body of a SIP request.
Although described as a protocol, SDP is more of a format for describing multimedia sessions.
Few organisations will eliminate circuit-switched PBXs in the near future. This means
connecting disparate networks together is an essential part of VoIP. The Media Gateway Control
Protocol (MGCP) handles this. It works in with both H.323 and SIP, either of which can provide
call control, while MGCP manages the connections between disparate technologies.
Once a connection has been made between two endpoints, voice data is broken down into
packets and transmitted across the network in real time. Creating realistically sized packets without
compromising audio quality uses one of several G-series speech compression algorithms. G.711 is
the most established algorithm for this purpose, but its 64Kbps bandwidth requirement is a
drawback. However, it is mandatory in H.323-compliant networks. Speech compression
algorithms with more modest bandwidth needs include G.729A, which offers some of the best
features for VoIP. It combines small packet sizes with the voice quality of G.711 and delivers a
transmission rate of 8Kbps.
As quality is so essential to voice transmission, delayed transmissions or dropped packets become
more apparent in this type of application than in data-related tasks. Two main protocols are used to
ensure effective real-time delivery. RTP Real-time Transport Protocol provides timestamp and
control functions, ensuring data is reassembled in the correct order at its destination. Data is
buffered at the receiving so it is replayed at a constant rate, eliminating jitter. Its components
sequence numbers, used to find lost packets
payload identification, describing the media encoding used, which enables it to adapt to changes in
timestamp, used by the receiving client to 'play' the packet using the same timing used during
transmission. This should detect and compensate for delay jitter.
However, RTP does not provide any congestion or reliability control, and is not sufficient on its
own to ensure effective transportation.
RCP Real-time Control Protocol complements RTP by monitoring the quality of the end-to-end
link. RCP packets and RTP packets are mixed and sent between senders and receivers. The RCP
packets provide feedback on data transmission quality, and help identify any problems. RTP and
RCP work independently of the underlying transport layer. RTP uses UDP rather than TCP, as it is
better for real-time traffic.
Bandwidth management. Limited bandwidth, latency and network congestion are major
problems for VoIP implementations. H.323 has some integrated bandwidth management
capabilities, but both this older protocol and SIP can work with more modern alternatives such as
Resource Reservation Protocol (RSVP). It enables the sending mechanism to request a specific
level of service across the network. Each node across the network path between sender and receiver
is contacted to reserve network bandwidth.
RSVP alone is not sufficient to guarantee QoS. Other, more generic measures are also required.
These could include Type of Service (ToS), also referred to as IP Precedence and Differentiated
Services. Both data and voice applications can be managed using these features.
Network requirements for VoIP are more stringent than those for a data-only setup. Packet
loss and delivery delays that would not be evident in a data application result in unacceptable
quality when applied to voice. This means the architecture and design of the network are more
important. Understanding component-level resilience to failure, establishing how the network can
reconfigure itself in the event of such a breakdown and ensuring alternative paths are built in are all
essential. Firewalls can also create bottlenecks, impacting QoS. As a result, redesigning a network's
architecture is often a precursor to enjoying the cost benefits of VoIP.
Virtual Private Network. Used for two applications: the first is to link
two or more LANs together, the second is to allow remote and mobile users to connect to a central
office network. In each case the Internet is used to provide the connection so providing a cheap
solution. A VPN prevents anyone unauthorised from accessing the network. A VPN must
authenticate remote users and sites and then encrypt everything that makes up the communications.
The encrypted data can be wrapped inside normal IP packets and routed across the Internet for
decryption by other gateways or client VPN software - a process known as tunnelling.
Authentication often uses DES (Data Encryption Standard), 3DES or AES (Advanced Encryption
Standard) algorithms. Key management often handled by IKE (Internet key Exchange). The
tunnelling protocol often uses L2TP (Layer 2 Tunnelling Protocol) in Windows 2000. Devised by
Cisco and Microsoft. L2TP uses IPSec (IP Security protocol from the IETF - Internet Engineering
Task Force). Does have trouble traversing NAT (Network Address Translation ) gateways. VPN
functionality is included as part of RRAS (Routing and Remote Access Service) in Windows 2000
Video random Access Memory. DRAM found on video controllers.
Can be accessed simultaneously by two devices, so that the digital to analogue converter
RAMDAC can supply screen updates while the processor is supplying data. Dual port so that it can
read and write data on the same clock cycle.
Virtual Reality Modelling Language, a set of codes used for writing
files in 3D. Requires a special browser to view.
Virtual Router Redundancy Protocol. Allows a collection of physical
routers to be viewed as one virtual router.
Very high speed Digital Subscriber Line. Offers 14Mbps down
stream and 3Mbps upstream, over fibre connecting BT's exchanges to street cabinets.
Volume Shadow copy Service - MS Windows 2003
Virtual Studio Technology. Music editing technology - first
implemented by Steinberg and made open source.
Virtual Device Driver. A special type of device driver that has access
to the core of the operating system for supervising hardware operations directly. A mouse, serial
port and parallel port use VxDs.
World Wide Web Consortium. The forum for addressing Web related
issues. Set up in 1994.
Web Accessibility Initiative
Wide Area Information Servers
Wide Area Network. Spans a wide geographical area, linking
together LANs, e.g. JANET.
Wireless application protocol. Designed to allow Web content and
other services to be sent directly to mobile phone displays. Supported by Motorola, Nokia and
Open Node
Identify the zones of unsecured wireless networks.
Closed Node
WEP Node
-Wavetable Synthesis
The successor to FM synthesis, wavetable synthesis can store samples
of musical instruments and can use them to generate quite realistic sounding music.
Wideband Code Division Multiple Access
Wavelength Division Multiplexing. To increase the capacity of the
fibre, multiple wavelengths are used. As each fibre carries multiple wavelengths, need to ensure
that they are kept far enough apart to ensure that their dispersion does not cause the wavelengths to
overlap and interfere with each other. Lasers also drift so frequencies can shift.
-Web 2.0
Essentially describes what has been happening in the development
web in the specific period of time from 2001 to present. Includes dominance by major companies,
Amazon, Google, e-Bay etc
Web-Based Enterprise Management
-Web server
A computer that serves Web pages. On the request for a page, it
receives the request and sends the page back to the web browser.
An e-commerce server product from IBM. It creates e-commerce
sites and applications based on Java
Wireless Ethernet Compatibility Alliance - trade association created
to promote interoperability between different vendors 'WLAN equipment.
Waste Electrical and Electronic Equipment Directive. Puts the onus
on the manufacturer. The directive states that the rate of recovery of materials shall be increased to
a minimum of 75% by weight. The targets have to be met by 1st January 2006. The regulations are
due to come into place on 13th August 2005.
Wired Equivalent Privacy - the default encryption scheme used by
802.11x equipment and comes in either 40bit or 104bit key formats. A 24 bit random initialisation
vector (IV) is prefixed to the key to give the full key stream. This ensures that no two packets are
ever encrypted using the same key. Before being encrypted the data has a checksum calculated and
appended to the packet. This will ensure that the data is correctly decoded after transmission. Once
the checksum has been calculated the RC4 algorithm performs an exclusive OR between the full
key stream and data/checksum combination. The encrypted data is then sent across the network
with the IV transmitted in plain text. At the other end the receiver takes the IV and prefixes it to the
WEP key and performs another XOR. This reverses the encryption process and checks the
checksum. Uses static encryption keys.
Wired For Management. Intel's specification for automating client
Wireless High Definition Interface. Primarily designed to deliver
uncompressed data to flat panel televisions. It operates in the 5GHz band. Theoretical maximum
data rate is 1.5Gb/s
Whois search
Finds the name, address and details of a domain name's registrant
Windows Hardware Quality Labs certification - means that drivers
have been scrutinised by Microsoft's testers for compatibility with Windows OSes.
Windows Script Host. In Windows setup - Accessories. Disable to
stop Java and VB scripts running.
-Wide SCSI
A SCSI standard that transfers data at 40MB/s.
Web Interface Definition Language - an XML application to allow
web resources to be described as functional interfaces that can be accessed by remote systems using
standard web protocols.
802.11b networking standard
-Wild virus
A virus in circulation. Currently there are about 250 wild viruses in
the world.
A new wireless broadband technology that promisesup to 70Mb/s
over distances of up to 30km. It will support advanced encryption systems from the beginning.
Uses the 802.16 networking standard. Uses signals in the 3.5 and 5.8GHz band. Current power
limit is 2W.
WiMax technology based on 802.16d and in the near future 802.16e.
Windows, Icons, Menus, Pointers
Concerned with the use of high memory. Provides backwards
compatibility with Windows 3.0. Not needed for later versions.
-Windows key*
shift, m
System properties
Go to desktop
Open My computer
Minimise all windows
Restore all windows
Disposable temporary files: ~*.*, _*.*, *.??_, *.??~
Needs Times New Roman, Arial and Courier.
Win95 - right click any item for a menu of common commands that apply to it.
To make toggle keys sound when pressed; Control Panel, double click Accessibility options,
select Toggle keys and click OK.
PrintScreen key captures the entire screen to the clipboard, Alt Print Screen captures just the
current window or dialogue box.
EDITING Msdos.sys (Remember it is Read Only!!) Use attrib -s -h -r msdos.sys before
editing and then attrib +s +h +r msdos.sys after.
It is in the root directory of the start up drive. Under Options;
BootMenu=1 forces windows to display a menu of options each time the computer is started. Press
the required letter to select. If no choice is made then windows will select the default. To set the
default use BootMenuDefault=(number). To determine how long Windows waits before using its
default time of 30s, type a line like BootMenuDelay=10 which will make it delay 10s.
Bootdelay=0 will give the Startup menu as soon as possible.
Change BootGUI from 1 to 0 to stop windows booting automatically.
Only OSR2 runs Scan disk automatically after an improper shutdown.
Never run scandisk
Run scandisk after prompt
Run scandisk without prompt
Show W95 logo screen
Don't show logo screen (Can fix some incompatability problems).
Old DOS version.
Startup Menu
DOS sets an environment variable %Config% to the name of the menu item that was chosen; this is
the short name that appears after 'menuitem='
The program that launches Windows is Restart the computer in MS-DOS mode. At the
C:\Windows prompt type ren
Win95 can access up to 4Gb of memory.
FAT16 can handle partitions up to 2Gb, by using clusters of 32Kb. FAT32 can handle partitions up
to 2Tb and can use 4Kb clusters up to partitions of 8Gb
System resources; composed of two heaps each of which is only 64Kb. (W95 has other heaps
which are not size limited). The closer either heap gets to being filled, the more unstable Windows
becomes. The two heaps are GDI, which stores images for onscreen displays, and User, where
programs keep windowing and other information. The Resource meter shows whichever of the two
is worse off at the current moment. The only way to clear a heap is to exit and then re-enter
Keyboard shortcuts.
Ctrl + x
to cut selected text.
Ctrl + c
to copy selected text.
Ctrl + v
to paste selected text.
Ctrl + g
for the goto option (in Windows Explorer)
Ctrl + z
to undo the previous action.
Ctrl + a
to select all files or text.
Ctrl + F4
to close the active document window.
Ctrl + F6
to switch between open documents.
Ctrl + Esc
brings up the Start menu.
Ctrl + Esc + r
to open the Run dialogue box.
Ctrl + drag a file
to a folder to copy a file.
Ctrl + Shift + drag a file
to the desktop or a folder to create a shortcut.
Ctrl as Windows restarts prevents Startup group applications from loading.
Shift + F10
to open task bar properties.
Shift + delete
to delete items without putting them into the Recycle bin.
Shift + inserting a CD
to disable Autorun
Alt + F4
to close a windows one at a time.
Alt + enter
to view the properties of a selected item.
Alt + spacebar
to access the window menu in any window.
Alt + spacebar + c
closes the active window
Alt + spacebar + m
moves the active window position using the arrow keys.
Alt + spacebar + n
to minimise the active window.
Alt + spacebar + s
resizes the active window using the arrow keys
Alt + spacebar + x
to maximise the active window.
Alt + tab
to toggle between open programs.
(in Explorer) goes straight to the parent folder.
Function keys.
to rename a selected file or folder.
to find a file or sub-folder.
displays the combo screen (in Explorer).
to refresh the screen.
to switch panes in Explorer.
for special boot menu option like Safe mode.
for menu access.
Deleting icons from the desktop.
Use Registry editor and get to Hkey_local_machine\software\Microsoft\Windows\fflCurrent
Version\explorer\Desktop\Namespace. From here, select an alphanumeric key in the namespace
folder and the keys corresponding icon name will appear in the righthand pane under data. When
you find the icon that you want to lose, right click its key in the left hand pane and select delete.
Close the Registry Editor, click on the desktop once and then press F5 to refresh.
W95 Version.
Right click My computer and select properties. Under the general tab is the version number.
original version.
original version updated with Service pack 1.
OSR2 (OEM Service release 2)
OSR2.1 adds universal serial bus support.
Resources kit.
Contains much useful information. CD:\Admin\Reskit\helpfile win95rk.hlp
Updates to W95.
To list updates to the system run Qfecheck.exe (in c:\Windows).
Windows95 Service Packs
It is free of charge.
To Print from Explorer.
Not a standard option. Can be added to the context menu by:-In Explorer, select View, Options,
then click on the File Types tab. Scroll down until you see the Folder type. Select it and click Edit.
In the Edit File Type dialogue click New. In the New Action dialogue enter a name for the action
like List or Print; this will appear in the menu. In the Application used to perform action field,
type: /c dir"%1" /o>prn Close all the dialogues and the new option now appears in
your folder context menus.
Duplicate files.
W95 creates a lot of duplicate files. In c:\windows\sysbckup it keeps copies of many files that are in
c:\windows\system so that it can replace these files in the event of an errant Setup Program. These
should NOT be deleted. For other files if one copy is in either c:\windows or c:\windows\system,
then you can safely delete any other copies. Windows will look in either of these places if the file it
needs isn't found in an applications home directory.
To prevent a CD auto running:a).
Hold down the shift key until the drive drawer is closed and Windows has read the
Control panel, System, CD ROM driver, click Properties, clear the box next to Auto
Insert notification, click OK and close.
Power toys for Windows 95: TweakUI control panel accessory. Enables the control of the windows
animation and many other aspects of the user interface.
From the DOS prompt Extract /l c:\windows himem.sys
The command extract/A /D filename l MORE lists all the Windows 95 cab files and
shows which one contains the file 'filename'.
The file extension '.ico' is used for shortcut file extensions. Essentially they are bit maps.
Win95 screens.
Windows is shutting down screen
It is safe to turn off your computer screen
Startup screen.
Root directory, 256 colours by 320x400 pixels
Screen Savers.
To prevent it operating in Win95 ensure that the Start menu is displayed.
Reclaiming Disk Space.
Files to delete:
unless it has todays date.
Though beware of system files.
These are index files that are built the first time you use Find to search
the help file.
To clear the Documents record go to c:\Windows\Recent and delete the files and short cuts.
Make Notepad a Send To destination.
Windows folder, find Notepad, position the left hand window pane so that the SendTo folder is
visible, then drag Notepad to the SendTo folder. Now select the SendTo folder, select the shortcut
to notepad.exe icon and rename the shortcut to just Notepad.
To view an unknown file type, right click the file icon then select SendTo Notepad.
Cannot remove an NT partition using the normal FDisk. Need to use Partition Magic or the
To remove a file association, double click on My Computer, then choose Options from the View
menu and click the File Types tab. Scroll down the list, select the file and click Remove.
Microsoft RegClean 4 will clear any dross from the registry.
Windows set up problems. Various switches available. Run Setup/?from the command line to list
these options.
/C=run without using the disk cache
/D=clean install, ignoring existing Windows installations (better to reformat!)
/ID=skip the disk space check
/IE=skip creation of a startup disk
/IH=skip the Registry validity check
/IM=skip the memory check
/IN=run Setup without the Network Setup Module. Not able to run Network connection after.
/IP=skip detection of unknown plug and play
/IQ=skip the check for cross linked files
/IR=skip the detection of system Bios
/IS=skip the ScanDisk disk check
/IV=skip the display of information screens during setup
/L=Loads a Logitech mouse driver instead of a Microsoft one
/M=suppress playing of WAV sounds
/N=run without mouse support
/NM=bypass CPU detection enables Windows to be installed on lower spec machine!
/Nostart=performs only the copy part of the installation not the setup.
/NTLDR=bypass check for existing operating system - prevents OEM versions of Windows from
being installed on a PC with an existing Windows installation.
/T:<dir>=specifies the location Setup will use for its temporary files.
/P<option list>=allows diagnostic options to be selected during Setup. Multiple options should be
separated by ; e.g. Setup/Pb;f where
b=enables Prompt before Mode, allowing you to choose whether to run each device detection
f=enables clean registry mode, which ignores info about previously detected hardware in the registry
(Win95 only)
i=bypasses detection of unknown plug and play Bioses and devices (those not listed in machine.inf)
j=installs ACPI support in Win98 only. Printer port may need reconfiguring using Bios setup before
ACPI will work properly.
The application programming interface (API) used in Vista. FX
stands for Framework Extennsion and WinFX is a literal extension of the .net Framework. It will
replace Win32.
The windows equivalent of the autoexec.bat file.
Deals with the software. Placing a ; infront of a line in Winini disables the line.
Windows Internet Naming Service
To boot to a DOS prompt. In DOS type Attrib -s -h -r msdos.sys
Edit msdos.sys
Change the line that reads BootGUI=1 to BootGUI=0
Save the file and quit edit.
Attrib +s +h +r msdos.sys
To run windows from the command prompt type Win
Windows 95 can read up to 4GB of memory.
To prevent the applications in the start up folder from loading at bootup hold down the shift key as
Windows loads.
American keyboards in Dos - add a line to the AutoExec.bat file KEYB UK
Hold down CTRL key and reboot to get to command prompt.
To access the Boot menu hold down the shift key during bootup.
To restore registry c:\ then run ScanReg.exe
Stop background utilities starting by holding down Shift while Windows starts.
Run Scandisk in DOS to speed up process.
To clean up the hard disk - right click C. Select properties. Click the Disk Cleanup button. Finds
all disposable files.
Speed up W98 If more than 64MB memory reduce swap files by:run sysedit, select system.ini. Scroll down to the section headed by the line [386Enh] and then add
a line at the end of the section ConservativeSwapfileUsage=1
There is a bug in W98 which causes summer time adjustment even if it is unchecked. This can be
overcome by setting the time zone to Casablanca.
System File Checker - used to check system files on W98. Run SFC.
If a system won't even boot to safe mode then boot from a boot disk and then type SCANREG/FIX
from the command prompt.
Useful for multitasking, added security, multiprocessor systems, runs
demanding applications, running SCSI disk arrays. Has its own filing system, NTFS. NT cannot
recognise FAT32 partitions on Win9x systems and vice versa. Will support FAT16 though.
Event viewer logs critical system activity including crashes. launch from Start, Programs,
Administrative Tools, Event Viewer. Colour coded, blue for information, yellow for warning, red
for error.
User Manager. Start, Programs, Administrative Tools, User Manager for Domains. Choose
Policies, Audit, Audit these events.
To kill an App in NT, right click the Taskbar and click Task Manager. Click the Applications tab
and select the hung-up program from the list of running tasks. Click the End Task button.
turns off the packet handling for network cards.
Under the registry key:
HKEY_LOCAL_Machine\System\CurrentControlSet\Services\TCPIP\Parameters create a new
DWORD value with a name of DisableTaskOffload and give it a value of 0.
W2000 server fully supported until 310305 - ends 310307
W XP Pro server fully supported until 311206 - ends 311208
-Windows XP
Recovery Console. Install from CD - Run - D:\i386\winnt32.exe/cmdcons
To disable a service, the command is
disable service_name/device_driver_name e.g. to disable the eventlog type disable eventlog
Batch files. Can contain any of the commands of the Recovery Console but cannot contain another
batch file. Syntax batch input_file [output_file] Output files are not necessary, but if specified
will store the results of the commands listed in the input file. If the output file is not specified then
the results are output to the screen e.g.
batch E:\myfiles\find.txt c:\mytests\results.txt
bootcfg/rebuild will attempt to rebuild the boot.ini file
Windows Internet Naming Service
A program that provides Windows with a standard way to
communicate with the Internet. Any Windows based PC needs one; often provided by the ISP.
Frequency bands available for short range devices in the UK are at
173MHz, 433MHz, 458MHz, 868MHz, 2.4GHz, 3.4GHz and 5.8GHz. 3.4GHz intended for
commercial providers to connect to homes. Intended to support a protected quality of service with
licences allocated to a number of regions. Could be used to support broadband beyond the reach of
ADSL and cable.
Wireless Local Area Networks - also known as WiFi. Europe uses
DSSS (Direct Sequence Spread Spectrum) on 13 different frequency channels on the 2.4GHz - ISM
band (Industrial, Scientific, Medical). There are only two combinations of a maximum of three
channels that can be guaranteed not to interfere with one another. These are 1-7-13 (most frequently
used in Europe)and 1-6-11 (most frequently used in the USA. The FCC - 2.4GHz ISM band is
shorter and does not contain channels 12 and 13.
The 2.4GHZ ISM band is from 2.4 - 2.4835GHz.
ETS 300328 (European Telecommunications Standard) limits the transmission power to 100mW at
1m from the aerial.
Windows Media Audio
Windows Media Video
Versions of Word earlier than 6.0c require the presence of the file
share.exe, even though it is functionally built into Windows 95 and Windows 98. Needs to be
placed into the root directory of C. Can use a null length file called share.exe to fool the program.
Settings file NORMAL.DOT.
Ctrl+Shift+z turns off sub and superscripts.
A sub-section of a larger network or a small LAN (up to 50 users).
Wi-Fi Protected Access. A subset of 802.11i A WEP replacement
that uses rotating keys.
Windows Server Clustering
Web Service Description Language. An upshot of XML. It provides
a mechanism through which a device newly connected to a network can announce its presence and
describe what it can do. Jointly developed by Microsoft and IBM, this is essentially the language
used by the UDDI registry.
Windows Scripting Host
Web Services for Remote Portlets
Wireless Transport Layer Security. Used on WAP phones.
Wide Wave Division Multiplexing
World Wide Web
What You See Is What You Get.
-WYSIWYG editor
Software such as MS FrontPage or Macromedia Dreamweaver that
helps you create a Web site.
CCITT (ITU) standard governing interface between DTE and DCE
for synchronous operation on public data networks.
CCITT (ITU) standard governing interface between DTE and DCE
terminals operating in the packet mode on public data networks.
-X.25 PAD
A device that permits communication between non-X.25 devices and
the devices on an X.25 network
10Gbps Ethernet Attachment Unit Interface. Used with 10GB
Ethernet MAC. Pronounced "Zowie"
Freeware BASIC interpreter.
Extended Development Environment
Extensible Hypertext Markup Language. The successor to HTML.
XHTML1.0 became a W3C recommendation in January 2000 and work on XHTML2 is well
Execute In Place. Software places on a PCMCIA ROM card can be
executed from the card instead of being loaded into RAM first.
Extensible Linking Language. Provides Hyperlinking in XML.
Extensible Mark-up Language. Similar to HTML as a language for
page construction. A meta language - used to describe other languages. Devised by the World
Wide Web consortium group. Open format. Meant to be readable by anyone. XML defines the
document structure itself. Contents should be visible in plain text. Any device with an XMLenabled browser can render a version of the same document but do so in a way specifically designed
for the device being used. XML interacts with the Document Object Model. XML is a subset of
A file transfer protocol. Transmits 128byte blocks and was the first
FTP for PCs. It performs a checksum on packets to help ensure accurate transmission. The sending
computer uses an algorithm that calculates the binary values in a packet and sends the result as a tail
on the packet. The receiving computer goes through the same algorithm. If the two sums do not
match, then it requests that the packet be resent.
See Extended memory.
Transmitter On/Transmitter Off. Control characters used for flow
control, instructing a terminal to start transmission (X-ON) and end transmission (X-OFF).
Extensible Stylesheet Language part of XML. Has three parts XSLT, which handles the transformations of one XML file into another. XPath, which is a
language used by XSLT to access or refer to parts of an XML document and XSL Formatting
Objects, which handles the actual formatting. More powerful than CSS.
Extra Technology. An IBM model designation now generally
accepted to mean any PC with a 8088 or 8086 CPU
A file transfer protocol. This transmits 1KB blocks and adds batch
file processing to Xmodem. Both Xmodem and Ymodem are stop and wait protocols. The sending
computer transmits, then waits to receive an acknowledgement from the receiving computer. A
NAK (negative acknowledgement) indicates a bad or missing packet and requests that the sending
computern resend the packet.
-ZIF socket
Zero Insertion Force socket.
(IEEE802.15.4) A very low power, limited range wireless system. It
defines a network mesh where multiple paths exist between nodes. This provides redundancy and
resilience. Designed for very low power drain and primarily used for industrial control and building
A file transfer protocol. This is a streaming protocol. The sending
computer sends packets until it receives a negative acknowledgement (NAK). It then backs up to
the bad packet and resends from there. Can also adjust packet size depending upon line conditions.
If interrupted it can restart and resume from the point at which it was interrupted. Often used for
satellite transmissions because of the changeable line conditions.
-Zone transfers
Requests to DNS servers for all available information. Should be
disabled for all except secondary DNS servers.
-Zoo viruses
Live mostly within research labs and have not escaped into general
circulation. Currently about 18000
Binary File Reader
File Analyzer
Hacker site
Internet glossary
Lock picking
Winsock Software. (The Ultimate Collection Of )
Win98 Magnify.
magnify.exe and mag_hook.dll. Put in any folder in Win95 machine.
DVD sites.
Free File decompression program - Aladdin Expander - Notepad+, Notemaid. turning off java script in e-mails.
Enables you to visit web sites anonymously. contains an article explaining how to play DVDs with
any region code using the Microsoft DVD player.
details on how to unlock DVDs
Free web based SMS messaging service Popcorn E-mail system
ZoneAlarm firewall
Basic Java Development kit from
Free versions of C, C++ and Pascal from dsniff network sniffing tools
Consumer Association
Office of Fair Trading
RAM computers
Government bug Y2K
Particle physics and physics web sites
New Scientist
on-line daily teachers newspaper.
Psion Dacom
Western Digital
Bios passwords: Killcmos. Useful site for finding out details of other web sites
Airsnort requires 5 to 10 million packets to be
gathered from a wireless LAN before cracking the key.
WLAN cracker
Kismet sniffs for unprotected WLANs
Wellenreiter sniffs for unprotected WLANs
version for Win32
Download version of Apache web server - choose
Security Scans
SMS to mobiles
Computer reference
Eliminate the need for on-line registration a free service which checks web pages
according to W3C standards and US Section 508 guidelines