Download Revision_cards

Computer System
Reliability
Disaster Recovery
How reliable systems are –
Planning what to do if there
Unreliable systems may have
is a disaster (fire, flood,
Anything that has a input,
legal impact, aircraft
natural disaster etc.). Making
output device, processor and accidents etc., loss of data, sure you detect, correct and
storage device
loss of use of systems
prevent problems by
backups, spare hardware,
impacting on business
failover, backup power
IPOS
Down time
When a computer system
isn’t running, the system is
down. It is important to
reduce the amount the
system is down especially
when we rely on them so
much
De facto
Open standards
Failover
Redundancy
Standards that just develop
by common use. They
become the standard way of
doing things (e.g.
Programmers using
Comments)
Standards that are publically
available.
Software keeps an eye on
the health of systems. If it
detects a problem it may
switch over to another
working system (mirror
system) and keeps the
system running
Keeping a spare piece(s) of
hardware in case one breaks.
Making sure there is no
system down time (or very
little)
Open source software is
publically available, experts can
use and change. E.g. Android,
Linux
No one to blame if things g wrong
CPU
RAM
ROM
CACHE memory
Processors instructions
Volatile memory
Non volatile
Uses a fetch - decode –
execute cycle
Holds the most recent
instructions that have been
processed
Holds the boot up program
used when the computer
first starts (boot strap)
Volatile memory located as
part of the CPU chip
Lack of RAM is a likely cause
of performance issues
Generally holds less data
than RAM. Manufacturing
costs higher than RAM
VIRTUAL memory
Clock Speed
Cores
Flash Memory
An area on the hard disk
used as memory. Used when
RAM is too small to deal with
the amount of instructions.
Effects the performance
Speed of the processor. E.g.
4GHZ - this means the CPU
can process 4 billion
instructions per
cycle/second
Dual core – This means two
Solid-state memory used as
low cost secondary storage
in portable devices and as
removable memory
Processing units in the CPU
Quad core – four processing
units per CPU
For example USB, SD , Micro
SD
LOGIC GATE - AND
LOGIC GATE - OR
Both inputs need to be on
(1) for the output to be on
(1)
One or the other inputs
need to be on (1) for the
output to be on (1)
LOGIC GATE - NOT
Truth Table
The output is opposite to A table that contains all of
the inputs and output
the input
combinations for a logic
gate
Hardware
Software
All the physical parts in a
computer system
Programs, apps
e.g.
motherboard, keyboard,
mouse etc
Software is the programs
that run on a computer.
File formats
Instructions and Data
When the CPU fetches data it
will be treated as an instruction
(something it has to do) or just
data (information)
INPUT devices
OUTPUT devices
Secondary Storage types
Hardware that allows data to Hardware that allows data to
be entered into a computer be output from a computer Magnetic – Hard disk
system e.g. Keyboard,
system e.g. monitor, printer
Optical – CD,DVD, BlueRay
mouse
Solid state – No moving
parts, USB, External hard
disk
Secondary Storage -
Secondary Storage
Secondary Storage
Durability
Portability
Reliability
How tough the storage is,
how easy it is to damage
How easy it is to move it. E.g.
CD is easy to carry around,
USB is lighter. Hard disk
heavy and inside the
computer
Does the hardware work or
does it break down easily?
Can you reply on it?
e.g CD can be scratched,
Hard disk more durable
Secondary Storage
Non-volatile method for
storing large amounts of
data for long term use
e.g. Hard disk, USB, SD card,
Micro SD
Used to store progams and
data, other files
Secondary Storage
Sizes
Magnet hard disks – large
capacity, (GB/TB)
Optical disks – (CD/DVD) holds
large programs, videos, relatively
slow but inexpensive 700mb (CD)
4,7GB(DVD)
Flash (solid-state) – relatively
inexpensive and good access
times, can hold many GB of data
Binary Units
Binary to hexadecimal
Split the binary into nibbles
Binary to denary
Hexadecimal to binary
Denary to binary
Binary addition (Overflow)
Place a 1 under the correct numbers
that add up to make the number
When you add numbers
together and the answer
won’t fit into the number of
binary digits (you need an
extra
binary
digit)
Hexadecimal
Sound sampling
Why do we use hexadecimal Storage sound
numbers? Binary numbers
Size file - interval
get very big and difficult to
use. It is easier for
programmers to convert
between binary and hex
than binary and denary
Character sets
Metadata
Resolution
Colour depth
A standard that converts all
characters on a normal keyboard
into binary codes for the
computer to understand
Information about the image
that allows a computer to
recreate the image from
binary
Describes the quality of an
image. Measure in DPI (dots
per inch)/pixels
Refers to the number of bits
used to represent the colour
of each individual pixel
Proprietary standards
Industry standards
UNICODE
ASCII
Standards owned by a
company. For example
products/software made by
Microsoft way work in a
specific way. This will be
different to Apple products
for example
Mostly hardware standards
that lots of companies agree
to follow. For example USB
An industry-standard
character set that can
represent thousands of
different characters
A relatively simple character
set that can represent 128
different characters
e.g. ASCII and UNICODE
The higher the resolution the The more colours, the more
e.g. the height, width, colour bigger the file size (and the bits needed so the larger the
more space you need to save file size (and the more space
depth
it)
you need to save it)
Database – Validation
The automatic checking of
inputted data by a computer
system to ensure it is
sensible, no erroneous data
is entered
e.g.
Range check –1-10
Presence check – “Required”
Off the shelf software
 Relatively cheap, (compared
to custom written software)
 Easily available from most
computer shops
 Thoroughly tested so there
won’t be any serious
problems or bugs

Lots of user support i.e. user
guides, online help and
forums
Operating system
Memory management
User interface
Multitasking
Peripherals
Security
Windows,Android,IOS,Linux
Open source software
 Free to use
 If you have skilled
programmers to hand, the
source code can be adapted
to suit your particular needs
(that is what 'open source'
means)

May not have as much bugfixing support and security
patches as commercial
versions
Utility
programs
DO – Disk organisation tools –
defragmenter (reorganise hard disk
and puts all of the free space
together)
SM – System maintenance tools,
system cleanup,auto updates,anti
spyware
S – Security – Firewall, antivirus
Proprietary software
Proprietary software legally remains
the property of the organisation,
group, or individual
 Stable product – reliable,
lots of bug fixes
 Support in a timely
manner – updates, help
 Usability – standard
interfaces, features
Custom written software
Software written specifically for
you
 The company will get the
exact software/system
that they need
 The software will work
exactly how they want it
to work
 Only has features that
they specifically need in
their business.
Open source – things to
discuss
QLEF
Database
DBMS
Entities and tables
Database – Key files
POSD
Separation from apps
and benefits
Entity - An object or thing of
importance about which
data is captured
Foreign key - A field used in
one table to represent the
value of a primary key in a
related table
Primary key - A field in a
table which uniquely
identifies each record in that
table
persistent, organised store
of data in electronic form
Custom data handling
Table - A set of data
elements organised in fields
and records
Database – Forms
Database – Queries
Database – Reports
Database – Modules
User interface tool which
allows a user to enter or
change data in a table
Database management tool
used to retrieve information
based on specified criteria
Database management tool
used to present information
to the user in a professional
way
Database software and
languages contain modules pre-written programs.
SELECT * FROM PUPILS
grade > C
[Make] = "Ferrari" AND
[Price] < 8000 "
Networks
Hubs/Switches
Wireless access points
Client server
More than one computer connected
together
Hub - broadcasts data to all
devices on a network. This can
use a lot of bandwidth as it
results in unnecessary data being
sent - not all computers might
need to receive the data.
Switch - stores the MAC
addresses of devices on a
network and filters data packets
to see which devices have asked
for them
A networking hardware
device that allows a Wi-Fi
compliant device to connect
to a wired network (part of
your Wi-Fi router)
Network type where a computer
is a server and others are peers.
Peer to peer
WAN
LAN vs WAN
IP address
Network type in which every
computer can act as a client
or server, with no central
servers
A computer network that
spans a relatively large
geographical area. Typically,
a WAN consists of two or
more local-area networks
(LANs)
A local area network (LAN)
is a computer network that
interconnects computers
within a limited area such as
a residence, school,
laboratory, or office building
Unique number assigned to
every computer or device
connected to the Internet
 Share files and devices
(e.g. printers)
 Site (software)licences
are likely to be cheaper
than buying several
standalone licences
 Users can collaborate
(work together)
Server - Software that provides
services to a client, or the
hardware that is running it,
Client - Software or hardware
that requests services from a
server
Network topology
Network topology
Network topology
Standalone
Bus – label the
terminators, server,
workstation
Ring – label the server,
cable, workstation
Star – label the server,
hub, cable, workstation
A computer that is not
connected to a network
All software is installed on
the standalone computer.
It doesn’t share peripherals
with any other computer
Network topology
Network topology
Network topology
TCP/IP
Bus
Ring
Star –
TCP/IP (also known as the internet
protocol suite) is the set of protocols
used over the internet. It organises
how data packets are communicated
and makes sure packets have the
correct data (so they can get to their
destination without a problem)




easy to install
cheap to install, as it doesn’t
require much cable
if the main cable fails/damaged
whole network will fail
more workstations are connected
the performance of the network
will become slower because of data
collisions


can transfer data quickly, even if
there are a large number of devices
connected because the data only
flows in one direction, so there
won’t be any data collisions.
If the main cable fails or any device
is faulty then the whole network
will fail.


very reliable – if one cable or
device fails then all the others will
continue to work
high performing as no data
collisions can occur

very reliable – if one cable or device
fails then all the others will continue
to work

expense to install
MAC address
DNS server
A unique number permanently
assigned to every physical
interface on a computer network
(the serial number of the network
hardware)
Computer within an ISP
network responsible for
matching up host names to
IP addresses
HTML
Compression
The computer programming
language hypertext markup
language used for displaying
web pages in a browser
The process of reducing the
physical size of files
Lossy – some of the quality
of the original file is lost
Lossless – none of the
original file quality is lost
Internet
Router
A worldwide collection of
computer networks
Device that forwards data
packets to the appropriate
parts of a computer network
WWW - The world wide web is a
collection of webpages found on
a network of computers
(internet). Your web browser uses
the internet to access the web
Algorithms
Test data
A series of steps designed to
solve a problem
The data you use to test part
of your program
e.g To test a maths quiz you
might enter “24” or “4.2” normal data
or “Bob” – erroneous data
Flow charts
High level language
Machine language
Translator
Diamond – Decision
Parallelogram – Input/Output
Rectangle - Process
Programming languages
which are similar to natural
languages
Binary instructions used by
the CPU
Converts high level
languages to machine code
Assembler
Compiler
Interpreter
IDE
Utility which converts low
level code into machine code
Utility which coverts high
level code into low level
code, whole blocks of code
at a time
Utility which coverts high
level code into low level
code, one line at a time
Software which provides a
number of dedicated tools
for software developers
(IDLE in python)
 Error diagnostics
 Run time environment
 Translator
 Auto documentation
Converts assembly language
into machine code
ADD 02EA
 Compiled program runs
very quickly.
 Difficult to find errors
Syntax and execution errors can be quickly
identified
Variables and constants
Variables
A value stored in memory
that can change while a
program runs
Constants
A value stored in memory
that cannot change while a
program runs
Pseudocode
Data types
Real(float) eg 10.3, 12.5
Integer eg 10,12
Boolean eg True/False
Character eg A, space,!
String “Hello world”
Pseudocode
For everything within the “grade”
If 4 is less than 5
Add 5 to 4
Print the result
Otherwise
Print "no"
Case based on Grade
Case >=100
Report “Perfect Score”
Case > 89
Report “Grade = A”
Lists and Arrays
Errors
Array - (like a list) is a series
of memory locations – or
‘boxes’ – each of which holds
a single item of data. All data
in an array must be of the
same data type
List - data structures similar
to arrays that allow data of
more than one data type
Syntax - A type of error that
occurs due to incorrect
spelling or grammar in a
program
Pseudocode
Pseudocode
Logic - A type of error that
occurs due to incorrect
algorithm design
Ethical
right and wrong as far as
programmers are concerned:
 Don’t take bribes
 Don’t do tasks you
cant do a good job of
 Avoid injuring others
 Don’t hard the
profession
Environment
 Energy – energy used by
computers, air
conditioning, thinking
about sustainable
resource/environment
friendly, reuse equipment,
make things reliable
 Disposal of equipment –
recycle at the
environmental centres as
they can be hazardous
Legal
Legal
Computer misuse act
(hacking/theft)
Data protection act
 Unauthorised access to
computer material
 Unauthorised access with
intent to commit
Unauthorised modification
of computer material.
 Making, supplying or
obtaining anything which
can be used in computer
misuse offences.
The Data Protection Act (DPA) is a
law designed to protect personal
data stored on computers or in
an organised paper filing system
Find out the 8 principles