Download Networking and the Internet – Glossary

Networking and the Internet – Glossary
This document is based on an idea from the class of 2004, and a starting list by Stephen White.
ACK
ACKnowledgement. Response to a flow of data that acknowledges safe arrival of
that flow. This confirms that the data has been received, and in practice, allows the
sending system to delete its record of the data, freeing up a buffer for further
transmissions. See also NAK.
ADSL
Asynchronous Digital Subscriber Line. Facility for sending (fairly) broadband
digital signals over standard twisted pair local phone lines, while allowing the lowfrequency capacity of the line to run as a normal phone line. Faster versions of
ADSL are available close to exchanges and over higher-quality local loops.
AOR
Application owning region: see FUNCTION SHIPPING.
API
Application Program Interface. Collection of callable subprograms that can be
used by an application to make use of middleware or operating system function.
For example, Windows provides an API that all programs must use if they wish to
communicate through the display or the keyboard.
APL
A Programming Language. Interpretive language developed in IBM Washington
Systems Center, which became heavily used for scientific, financial and analytical
programming. Largely superseded by spreadsheets.
ARPAnet The precursor to the Internet. Developed by the Advanced Research Projects
Agency for the US Department of Defense.
ASCII
American Standard Code for Information Interchange. Standard mapping of
characters to binary values of a byte (or traditionally, a 7-bit grouping). Used to
describe a closely related set of encodings that are almost universal on PCs, Macs,
workstations and mid-range servers. See also EBCDIC.
ATM
1) Asynchronous Transfer Mode. High speed transmission technique used mainly
over optical fibres to connect routers. The backbone of MANs, and the underlying
technology used by BT to support connections between ADSL connections and the
Internet.
2) Automated Teller Machine. Bank workstation offering facilities direct to the
public, and usually including the ability to draw cash.
BACS
Bankers Automated Clearing System. UK service used to transfer funds between
banks. The basis of most direct payroll systems, and foundation of EFT.
CCITT
Comité Consultatif International Téléphonique.
Guardian of international
communication standards such as the V.34 modem standard. Now called ITU.
CDFS
see FILE SYSTEMS
CICS
Customer Information Control System. Leading transaction processing middleware, running mainly on z-Series mainframes, and allowing them to connect to
transaction servers on Unix and Intel systems. Licensed on over 95% of all
mainframes, and used to provide data integrity in distributed systems.
COBOL – COmmon Business Oriented Language. Early high-level language developed by
Captain Grace Hopper of the US Navy around 1957, to extend programming from
the scientific to business community.
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CPU
Central Processor Unit. Collection of electronic circuitry capable of running a
program. Usually consists of an Instruction Counter that contains the address of
the next instruction to be run; one or more Arithmetic and Logic Units (ALU) that
do calculations and comparisons; and a set of accumulators or Registers that hold
intermediate results.
CRC
Cyclic redundancy check. Form of redundancy that uses an algorithm acting on all
the bytes in a block. Since this could potentially produce very long numbers, these
are expressed by counting up to the limit, then starting again at zero.
CSMA/CD Carrier Sense Multiple Access with Collision Detection. The standard that makes
ETHERNET local area networks operate. Before broadcasting a message, the
network card “listens” to the wire that connects it to the LAN, and sends only when
it senses that there is no other traffic. A “collision” occurs if another node is doing
the same thing, and transmits at the same time. Nodes detect collisions by
comparing what’s on the wire with what they have just sent, and back off when a
collision occurs. By waiting a random time before retrying, the standard reduces
the chance of repeated collisions, but this approach still limits the capacity of an
Ethernet LAN to approximately 40% of its rated speed.
CSS
Cascading Style Sheets. Facility to produce a consistent look and feel across web
sites by defining the mapping between tag and appearance separately from the
pages themselves. Pages can refer to a CSS, thus picking up the defaults stored in
that sheet, without any need to know what they are.
DAT
Digital Audio Tape. Recordable equivalent of CD, though with a 48KHz sample
rate. Like CD, it is uncompressed and offers 16-bit resolution on each channel.
DAT uses a helical recording technology similar to a video tape, which gives a
high capacity, making it suitable for use as a backup device for computer systems.
DBCS
Double-Byte Character Set. Any character set with so many characters that it
cannot be specified with a single 8-bit code. The most common DBCS is Unicode,
which allows text to be expressed in Latin, Greek, Cyrillic, Arabic, Hebrew, and
multiple Asian scripts, without the need to “shift” in and out of different encodings.
Mainframe DBCS differ from Unicode, but also allow mixtures of (say) Kanji,
Greek and Roman within the same display.
DCC
1) Direct Cable Connection.
2) Digital Compact Cassette. Philips attempt to enter digital recording market, with
a linear tape technology compatible with the earlier Musicassette form-factor. It
was excessively compressed compared with MiniDisc, and never took off. See also
DAT.
DMA
Direct Memory Access. Feature whereby a peripheral processor (like an I/O
controller) can read and write directly into memory, without the need to pass the
data through the CPU. Implemented on IBM mainframes by Channels, on ICL by
Autonomous Transfer Units, and on all modern computers. Clashes of DMA
addresses were a major source of hardware incompatibility on PCs before the
advent of USB.
DoD
(US) Department of Defense. Sponsors of the Advanced Research Projects Agency
(ARPA) and thus of the network protocols that developed into the Internet.
DOS
Disk Operating System. Once a low-end operating system on the IBM 360 and
370 series, but now mainly used of Microsoft and IBM’s original systems for the
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IBM PC, managing Intel 8088 and 8068 CPUs. This is a simple, single user
system with ability to SPOOL printing, but not to support multiple user processes.
DTR
Data Terminal Ready. MODEM status when ready to accept or initiate calls.
EBCDIC
Extended Binary-Coded Decimal Interchange Code. Functional equivalent to
ASCII, but defining how characters map on to byte values on a mainframe
computer. Now virtually confined to IBM z-Series and its clones.
EDI
Electronic Data Interchange. Support of transactions over a network, private or
multi-user.
EFT
Electronic Funds Transfer. Any facility used to support payment between
enterprises, including those used by retailers to obtain payment from customers’
bank accounts.
Ethernet
The most common form of LAN, based on IEEE 802.3 standard for CSMA/CD.
Theoretically a shared bus, though usually implemented as a set of twisted-pair
wires from each device to a central hub or switch. Most commonly run at
100Mbps over Category 5 wires (100BaseT) though Gigabit Ethernet is becoming
more common and some 10Mbps LANs still exist (10BaseT).
File System: How space on a storage medium is organized to be written and read by an
application program, and the operating system support needed to control hardware
and manage space. All modern file systems are hierarchical, and allow you to
create named subdirectories to put files into, thus structuring the file store.
Common file systems on Windows are:
 FAT (File Allocation Table): a system that divides a disk into up to 64K
allocation units, each of which can contain up to 32K bytes (thus setting an
upper limit of 2GB to the size of the disk). File name was limited to 8
characters, and file type to 3.
 FAT32: Like FAT, but with 32-bit codes for identifying allocation units and
their length, thus raising the capacity limit to many billions of GB. Allows long
file names and types.
 NTFS: Windows NT version of OS/2’s High Performance File System (HPFS),
used by all versions of Windows based on Windows NT, including Windows
2000 and XP. Allows long file names and types (HPFS allowed long names, but
restricted types to 3 characters).
 CDFS (Compact Disc File System): used on data CDs. Although the CD is an
inherently serial medium (with a spiral track from middle to outside) CDFS
emulates a normal directory-based direct access view of the data. The only
restriction you’re likely to come across is on length of file name (25 characters).
File systems similar to NTFS exist in UNIX and IBM’s VM systems. zOS has a
comparable file system called VSAM.
FOR
File owning region: see FUNCTION SHIPPING.
FireWire
Apple’s trademark for serial connections using the IEEE1394 standard. Sony also
market products based on the standard, which they call iLink (and deliver with a
non-standard, small connector that’s common on digital video cameras).
IEEE1394 runs at 400Mbps, slightly slower than the stated rate of USB2.0, but
nevertheless it seems able to deliver faster data transfer. The new IEEE1394b
standard defines 800 and 1600Mbps data rates.
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FTP
File Transfer Protocol. Application protocol used for bulk data transfer over the
Internet.
Function Shipping CICS terminology for handling a request for data held outside the system
running the application program. This is used so that multiple AORs (Application
owning regions) can work on the same datasets without risk of violating the
integrity of the data.
GB
Gigabyte. 230 bytes (1024MB, or 1,073,741,824 bytes). For disk drives, the term
is misused to mean a billion bytes (109 bytes), which is why when you buy a
107GB disk, Windows only reports it as 100GB.
GSM
Global System for Mobile Communications. The second generation mobile phone
technology, digitizing speech so that it can be sent as short packets to the local cell
transmitter, then packet-switched over the network.
GUI
Graphical User Interface, pronounced “gooey”. The implementation of the WIMP
paradigm.
HDLC
High-level Data Link Control. The OSI data link protocol, modelled on SNA’s
SDLC. Never commercially viable.
HPFS
see FILE SYSTEMS
HTML
HyperText Mark-up Language
HUB
Box allowing the connection of several devices to a single USB cable or Ethernet
LAN. The aggregate data-rate of all the devices is limited to the speed of the initial
connection. The main virtue of Ethernet hubs is to simulate a bus while allowing
each network card (“node”) to be connected by a single cable, with the hub
protecting the integrity of the bus by disconnecting any cable that creates problems
– compare this with thin Ethernet, where a defective connection to one client could
bring down the whole LAN. Ethernet connections to a hub are usually by RJ45
plugs (unlike the BNC plugs and T-pieces used on a thin Ethernet bus). Because
the connection from the hub to each node is by a radial cable, there is no need to
send every byte on the LAN to every node – we could send only those packets
intended for the node. If that is done, it is possible to run two flows through the
hub concurrently, with a data-rate that exceeds that of the LAN. The benefit tends
to be limited, because the connection to a server used by many nodes will still be a
bottleneck. Hubs that offer this extra feature are called Switches, because they
switch the packets rather than simply duplicating them.
IC
Integrated Circuit. A section of silicon wafer on which is printed an entire circuit,
consisting of transistors, diodes and other components. Because the components
are so close together, ICs are much faster than the same function implemented with
discrete components, as well as being a fraction of the cost.
IDE
Integrated Disk Electronics. Originally a description of where the electronics to
control a disk drive were located, but later used to distinguish commodity DASD
from the higher performance SCSI disks used on Servers and workstations. IDE
disks have traditionally communicated in parallel over a 40-wire ribbon cable, but
are now available in a faster serial version.
IEEE
Institute of Electrical and Electronics Engineers. Provider of standards including
IEEE 802 for Local Area Networks, such as Ethernet (IEEE 802.3) and Wireless
(802.11) For the standards, see http://standards.ieee.org/getieee802/portfolio.html
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IMS
Information Management System. An early database system that used a
hierarchical model. IMS included a data communications component (IMS/DC),
but was almost always used as a database behind CICS applications.
IP
Internet Protocol. The networking layer of TCP/IP, which controls long-range
routing over the Internet and comparable networks.
IR
Infra-Red. Used of wireless connections that modulate an infra-red beam, in a
similar way to the common TV remote control. Formerly fairly common for
connecting printers to notebook computers, but now being superseded by Wireless
LANs. IR is a line-of-sight technology, whereas the GHz radio frequencies used
by wireless LANs can penetrate walls and furniture.
ISDN
Integrated Services Digital Network. Obsolete digital service to subscribers,
supporting two 64kbps channels (plus a control channel) over a single circuit to the
exchange. Fairly common in mainland Europe, where it was provided at a price
comparable with analogue circuits, but never successful in the UK or US. Its
failure in the UK was caused by high price (transfer at 128kbps was charged as two
calls, with the minimum call charge on each – and installation costs and line rentals
were high as well). In the US, the widespread availability of 1.5Mbps T1 circuits
made the service seem slow, despite the added convenience of being able to call
any ISDN subscriber. Now superseded by ADSL.
ISP
Internet Service Provider.
ITU
International Telecommunication Union (formerly CCITT). Guardian of such
international communication standards as the V.34 modem standard.
JCL
Job Control Language. Language used to allow users to define the prerequisite
conditions for batch processing. For example, to ensure that steps of jobs run in
sequence, and only when it is safe to run them. Also used for resource
management, to ensure that a step does not begin until the resources it needs are
available.
LAN
Local Area Network. Network within an enterprise, usually functioning by
broadcast from each station or node on the network. Nowadays means Ethernet, as
Token Ring LANS (to IEEE 802.5 standard) are now obsolescent.
MAU
Multiple Access Unit. The Token Ring equivalent of an Ethernet hub. Contains
logic to take a system out of the ring if the circuit or system fails.
MB
Megabyte. 220 bytes (1024KB, or 1,048,576 bytes). Also used loosely to mean one
million bytes (106).
MAN
Metropolitan Area Network. A high-speed network of LANs within a relatively
small geographical area.
MAR/MBR Memory Access Register and Memory Buffer Register. The MAR is used to feed
an address to memory, which responds by transferring the contents of the memory
cell so addressed into the MBR. This is a piece of high-speed storage that forms a
“window” between memory and the rest of the computer.
MBR
Master Boot Record. Area at the start of a “Boot disk” that contains the code
needed to get an operating system started.
MIME
Multipurpose Internet Mail Extensions. Encoding that allows arbitrary datastreams to be sent be electronic mail, despite the fact that it was originally designed
for 7-bit alphanumeric characters.
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MIPS
Millions of Instructions Per Second – more accurately, Meaningless Indication of
Processor Speed! It’s meaningless because different computer architectures do
wildly different things in each instruction. Complex Instruction Set Computers
(CISC) like zSeries mainframe processors and the Intel x86 processor used in PCs,
have a large number of machine-code instructions, each of which can achieve a
meaningful action. Another approach to CPU design is the Reduced Instruction
Set Computer (RISC), like the PowerPC used in Macintosh and IBM midrange
machines. In these, the compiler generates a large number of very simple machinecode instructions. For example, a multiplication that could be done in one
instruction on a CISC machine might be turned into a sequence of ADD and SHIFT
instructions when compiled for a RISC processor. Thus a 1 MIPS CISC machine
might be able to perform commercial work faster than a 10 MIPS RISC machine.
A more meaningful measure of speed is to consider the time taken to perform a
benchmark task, such as handling a debit and credit in a financial database. This
may correlate loosely with MIPS within a single computer architecture, but each
family of machines will correlate in a different way.
MQ
Messaging and Queuing. An asynchronous approach to distributed applications.
One application sends a message to another, which performs a service once the
message arrives. Improves reliability by forcing clean interfaces, and also by
making clear the need to cope with potential delays or timing problems between the
systems. A popular implementation is MQ-series, which contains an infrastructure
that guarantees that any message will be delivered once and only once (though it
makes no promises about when).
NAK
Negative AcKnowledgement. A code sent by the receiving end of a link to indicate
that a packet has not been received successfully, usually because a CRC has failed.
The opposite of an ACK.
Network Drive
In Windows, a disk drive or equivalent that is physically attached to a
different system to the one requiring to perform I/O operations on it. Network
drives can be accessed by the same application programming that is used to access
local drives, even when the local system does not contain support for the file
system used for the physical drive (this an NT4 system can read FAT32 files on
Windows 98, despite not containing FAT32 support; similarly, the W98 system can
have access to NTFS files on the NT4 system). This is done using a form of
FUNCTION SHIPPING, by which the operating system traps calls to network drives
and converts them into a message flow with the server that owns the physical drive.
The server system then issues the instructions needed to read or write the files it
hosts.
NFS
Network File System. UNIX name for communication support that allows a
programme on one system to interact with a file located on another system, usually
a server. The facility involves the operating system on the client system trapping
an I/O (input or output) request, and generating a system-to-system message that is
sent to the server system, which then carries out the request on the real data,
returning results to the client that made the request. Thus NFS is very similar to
the familiar Windows support for NETWORK DRIVEs, and with CICS FUNCTION
SHIPPING.
NTFS
see FILE SYSTEMS
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OS
Operating System. Program that determines the user perception of a system. It
controls the hardware, manages resources, encapsulates common functions, and
provides concurrent operation of multiple processes.
OSI
Open System Interconnection. International standard developed to break IBM
SNA’s dominance of the packet-switching market. Maintained the 7-layer design
of SNA (though with some name changes), but never offered a complete stack of
software to match the stack of protocols. Parts, such as the X.25 data-link protocol,
were successful, but OSI was never competitive with SNA. Then in the 1990s,
both were swept away by TCP/IP.
Packet Switching: The basis of all networks that share a circuit between multiple logical
connections. TCP/IP is the main packet-switched protocol for wide-area
networking, and most local area networks use Ethernet. The principle of packet
switching is to break up point-to-point messages into packets small enough to
travel without holding up other traffic, and label each packet with its destination
and source. Packets travelling between different endpoints can then be sent down a
circuit that moves them towards their destination – for example, a packet from my
home machine on the Pipex network can be sent towards www.winchester.ac.uk
over the circuits linking Pipex to the Joint Academic Network, which they will
share with any other Pipex user communicating with any .ac.uk domain.
The analogy is with the postal service, where we put messages into packets,
address them, and commit them to the shared carrier by dropping them into a postbox. The Post Office then sorts the packets and sends them over routes that gets
them closer to their destination, eventually ending on a round where a postal
worker delivers them to the intended letter-box. We hope that networks will
deliver their packets at electronic speeds, but most elements of the postal service
have analogues in the Internet. My point-to-point connection to Pipex resembles
my journey to the post-box, in that it carries packets for multiple destinations, but
takes them all to one place. Pipex’s Router acts like a sorting office, to determine
which route each packet will take thereafter, and may well send my packets on
diverse routes, sharing each of these with packets from other users. One entry to
Janet, their router acts as another sorting office, fanning packets out to the various
regional academic networks. These then route to the appropriate university LAN,
the “round” that delivers them to the chosen host.
PSW
Program Status Word. The IBM/360 (and zSeries) term for the status vector that
contains the information needed to restore the state of the processor to how it was
at the time of an interrupt. The interrupt hardware of S/360 and its successors
automatically swaps the active PSW for one that activates the relevant interrupt
handler, simultaneously saving the old PSW in an area of memory owned by that
interrupt handler.
PTT
Telephone company. A hangover from the days when telephone services outside
the USA were a monopoly of the Post Office. . US equivalent is “Telco.”
Term used by the International Telephone Union (ITU) in the days when it was
called CCITT and communicated in French. The French equivalent of the British
Post Office was called the PTT (Compagnie Poste Téléphonique et Télégraphique).
QIC
Quarter-Inch Cartridge. Obsolete magnetic tape technology used for backup until
the mid-90s. Leading vendors included Iomega.
RACF
Resource Access Control Facility. Mainframe security system that implements the
concept of authenticating a user, and then permitting that user access to resources
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that are defined as accessible to a user within certain defined groups. RACF was
introduced in OS/VS in the 70s, and forms the basis of most modern security
systems, including Unix and Windows NT/XP. The apocryphal interpretation of
“Removes Access Completely Forever” testifies to the difficulty of by-passing
RACF security!
RAID
Redundant Array of Inexpensive (or Independent) Disks. An approach to data
integrity that differs from the traditional mainframe approach of making every
component as near perfect as possible. RAID recognizes the fact that components
fail, and uses redundancy to protect data integrity across failures. In general, units
of RAID DASD can be removed when they begin to fail, and the RAID controller
will reconstruct the contents of the failing drive from the redundant data held on the
survivors.
REXX
Restructured Extended Executor. Mike Cowlishaw’s structured (and interpreted)
language that was adopted by IBM for automating operations in all its operating
systems. REXX was originally intended to replace the BAT-like command
language of CMS, but was then implemented on PC-DOS, OS/400, OS/2, AOX
and MVS, allowing command scripts to be portable between all these operating
systems. REXX is a very forgiving language, in which something that looks as if it
should work probably will. This makes it unsuitable for safety-critical uses.
RISC
Reduced Instruction Set Computer – see MIPS.
RPC
Remote Procedure Call. The network equivalent of a Call, whereby one program
calls upon another to perform a service, then to return control to the calling
program. With RPC, the call is intercepted by the OS or middleware, and passed to
another system on the network that is capable of providing the required service.
SDLC
Synchronous Data Link Control. Layer 2 of the SNA protocol stack. Introduced
concept of continuous-request data flows, where multiple packets could be sent
before the acknowledgment had been received from the first.
SISO
Shift-In, Shift-Out. An obsolete technique for mixing DBCS (q.v.) and SBCS
character sets. For example, a screen might be designed with text in a SBCS such
as Latin or Kana, but be capable of displaying names in Kanji. On the boundary
between the common text and the field to display Kanji, the data-stream would
“shift-in” to DBCS mode for the Kanji, then shift out back to SBCS. Largely
superseded by Unicode and other “pure DBCS” implementations.
SNA
Systems Network Architecture. The first commercially viable general-purpose
packet-switching architecture for heterogeneous networks. Developed in the mid70s by IBM, it introduced the 7-layer concept of networking. A SNA network
consists of Logical Units (LUs) such as programs, physical units (PUs) such as
terminals, organized into subnets. SNA suffers from a small addressing range, so
large corporations needed multiple networks, but was immensely successful from
around 1978 to 1995, when it started to be superseded by IP networks.
SPOOL
Simultaneous Peripheral Operations On-Line. Technique used to minimize the
impact of the vastly different speeds of electronic and electro-mechanical
components within a computer. Instead of programs writing directly to glaciallyslow printers and card-readers, they write to a SPOOL file on disk. The operating
system then manages transfer of the data from the spool file to the printer or other
slow device. Vital in multi-programming systems, as it allows each process to
write to a spool file, after which the operating system can print without the risk of
interlacing output from different processes.
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SQL
(pronounced “sequel”) Structured Query Language. Standard way to manipulate
relational databases, allowing selection, ordering and joining of data tables. Use
the SQL View of an Access query to see examples of SQL.
TCP
Transmission Control Protocol. The Line control layer of the Internet. Rarely
separated from IP.
TOR
Terminal owning region: see TRANSACTION ROUTING.
Transaction Routing CICS terminology for running a transaction on a system other than the
one that controls the dialogue with the user. Users are connected to a Terminal
owning region (TOR) which manages the conversation, and determines which
transaction needs to be run next. It then selects a suitable AOR (application
owning region) where that transaction can be run, and sends the user data to that
AOR. Since the most unreliable aspect of any information system is the
application program code, this approach greatly reduces the risk of failure in the
TOR, which is “the system” so far as the user is concerned. If an application
program fails, the TOR can re-try it, routing the transaction to a different AOR if
the reason for failure was an AOR crash. Similarly, performance can be enhanced
by selecting the fastest AOR from a pool of AORs capable of running the required
transaction – load balancing.
UART
Universal Asynchronous Receiver-Transmitter. The usual I/O controller chip for
the serial port of a PC.
URL
Uniform Resource Locator. Unique address of a resource on the Internet,
consisting of a protocol descriptor (like http://), a domain (like
www.winchester.ac.uk) and a resource on the domain (such as
/bm/courses/BS2911.BS2911-Glossary.doc).
USB
Universal Serial Bus. Interface introduced to facilitate attachment of I/O devices to
computers. Apple intended use of USB (and FIREWIRE) to remove the need to
open up the case of an iMac to upgrade it, and the idea was swiftly taken up for the
PC, where upgrading notebook computers had always been difficult because of
lack of standards as well as internal space constraints. Devices attached by USB
can obtain DC power through the connection, and operate in a mode comparable
with PACKET SWITCHING, in which each data flow is controlled by a header to
identify the device. This allows multiple USB connections to flow over a single
cable, by plugging them into a HUB. Three USB standards exist: USB1 is obsolete;
USB1.1 runs at up to 12Mbit/sec; USB2 runs at up to 480Mbps.
VM/370
Virtual Machine. Operating system for IBM System/370 and successors. Its main
component, the Control Program (CP) provided virtual machines – a user
environment in which every hardware feature of the real S/370 was emulated by an
equivalent virtual component. Thus the use saw virtual disks (known as
minidisks), virtual printers, card-readers, operator console, and memory. Any
program that would run on a real S/370 would run in a virtual machine, providing
an excellent test-bed for operating systems and system changes, and allowing
multiple operating systems to run concurrently on the same hardware. VM/370
included a Conversational Monitor System (CMS) that provided a simple user
interface for operating a virtual machine. Through the 70s and until the rise of the
Windows PC, VM was the main environment for interactive processing. Like
VMS, VM was a descendant of CP/67, developed in Cambridge, MA, in the late
60s.
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VMS
Virtual Memory System. Main commercial operating system for the Digital
Electronics Corp VAX series. Base on DEC System 10 and incorporating many of
the ideas developed in IBM’s CP/67 operating system. Significant today mainly as
the first incarnation of many ideas behind the kernel of Windows NT (and thus of
Windows XP).
VoIP
Voice over Internet Protocol. Digital telephony where speech is converted to
digital packets that are then routed over circuits running Internet Protocols, or even
over the public Internet itself.
VSAM
Virtual Sequential Access Method. The main file system on IBM operating
systems for the zSeries mainframes, including MVS and zOS. The file store is
divided into allocation units that can be accessed sequentially or through an index
associated with each file in the store. Data is placed into units chosen to optimize
speed of access to the data.
WAN
Wide Area Network. Network extending off the premises of an enterprise, usually
by operation through circuits provided by a PTT.
WEP
Wired Equivalent Protection. Encryption technology for Wireless LANs that
claims to match the security of a wired LAN. In fact, the encryption can be broken
by brute force in under 10 minutes, so you are advised to switch to WPA.
WiFi
Wireless fidelity. Wireless LAN technology defined by IEEE standard 802.11b
(11Mbps), 802.11g (54Mbps) and later developments.
WIMP
Windows, Icons, Menus, Pointers. The paradigm developed at Xerox PARC (Palo
Alto Research Center) in the 1970s, that forms the basis of today’s graphical
operating systems, including Windows, MacOS, OS/2 and X-windows.
WPA
Wi-Fi Protected Access. There are two varieties, using keys that change over time
(TKIP) and a more secure flavour called Advanced Encryption Standard, which is
the default in WPA2. If your hardware supports it, you should always select
WPA2. For further details see
http://compudent.blogspot.com/2006/09/wireless-wep-vs-wpa-vs-wpa2.html
XML
Extensible Markup Language. Extension of HTML to allow content to include
definitions of tags and how they should be interpreted.
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