F451 AS Computing
Essential Knowledge
Term
Definition
Example
Hardware
Physical components of a computer system
Monitor, Base Unit
Software
Programs that allow the user to perform a task
Input Device
hardware that is used to put data into a computer
Mouse, Keyboard, Scanner
Output Device
hardware to display/report information from a computer
Projector, Printer
Storage Device
Stores data that has been collected for future use
Hard Disk
Secondary Storage Device
Peripheral that allows storage of data over a long period of time
Memory Stick
Application Software
Programs that allow user to do something useful/perform a useful task
Spreadsheet, Word Processor
Systems Software
Controls the hardware of the computer. Gives a platform to run other
software.
Sensor
Input device that detects physical quantities
Thermistor
Actuator
Anything that gives a physical output
Pump/Motor
Data
Raw Facts and figures
Information
Processed data that has meaning/context
External Components
Components that are outside the system unit of a PC
Printer
Internal Components
Components that are inside the system unit of a PC
CPU, RAM
RAM
RAM is Random Access Memory is a volatile. Contents are lost when
powered off. It contains applications software being used and data used
in the operating system. Changes to RAM are made as the device is being
used, and access to RAM is very fast
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ROM
ROM is Read Only Memory and is non-volatile. The contents are not
erased when powered off. The ROM contains the start up program which
allows a device to boot up the OS. The start up program is needed
immediately when the device is powered on. The contents of ROM cannot
be changed.
IAS
Immediate Access Store - RAM
GUI
A GUI is a graphical user interface which uses WIMP. A GUI is very
processor intensive.
WIMP
Window Icons Menu Pointer. 4 components of a GUI.
CLI
A CLI is a command line interface. The user has to type in specific
commands to operate the system. The user needs to be computer literate
to use it as they have to remember all the commands and their syntax. CLI
requires very little processing power.
Menu Driven Interface
A menu based interface is a list of on screen choices which leads to
further menus which allows the user to choose an action from a set list of
options. Does not allow user to access other parts of software. These are
commonly used on a touch screen information terminal or a mobile phone.
A menu based interface is easy and intuitive to use and requires little
training or computer literacy.
Mobile Phone. Touch screen information terminal.
Natural Language Interface
A natural language interface is where the user communicates with the
computer in a human conversation type way. Used with some internet
search engines and expert systems. Requires no training or computer
literacy. Very difficult to program due to the ambiguous nature of human
language.
Expert System
Expert System
Advanced piece of software used to provide an answer to a specific
problem. Often used in medical diagnosis and fault repairs on hardware.
Consists of a Knowledge Base, Inference Engine and a HCI (usually a
natural language interface)
Inference Engine
Interrogates the knowledge base to find an answer to a problem as part of
an Expert System.
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Knowledge Base
Experts in the field are interviewed to get information to create a
knowledge base. The rules used to interrogate the knowledge base are
collected in the rules base .The rules are used to interrogate the
knowledge base using a set of algorithms stored in the inference engine
Batch OS
Often run during night time/weekends
No need for human to be present
Run in computer downtime when workers have gone home
No need for instant response to inputs
Processes large amounts of data in one go
Similar data that requires similar processing
Operating System
Used to control the hardware of the system/resource management through
software like hardware drivers/system software. Provides platform on
which applications can run. Handles storage/management of files.
Provides a user interface. Allow communication between user & hardware.
Has utility programs used to carry out housekeeping on system.
Utility Software
Housekeeping programs which perform a common task. Programs to help
the running of the hardware and protect the system.
File handling Software
Allows storage of files on secondary storage devices. Uses
folders/directories/file extensions. Allows opening files/folders to retrieve
data. Copying of files from. Deletion of files from storage. Allows security
of files where needed.
Real Time OS
Data is processed instantly. System responds instantly to changes in input
Multi user OS
Allows more than 1 user to use the system simultaneously – e.g. a
network operating system. One computer with many terminals allows more
than one user at a time to access a central server. Each terminal given
time slice... in turn - each time slice very small (1/100 of a second). Time
slice cycles around each terminal at high speed allowing apparently
simultaneous access to all users. Data is separated from terminals. Must
have security provision/ individual user rights.
Processing cheques/bills/pay rolls
File handlers, Anti virus, Compression software
Automatic Pilots on airplanes. Seat booking system –
ensures 2 seats aren’t booked simultaneously
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Multi Tasking OS
Allows more than one task to run apparently simultaneously. Each task is
given an amount of processor time before going onto the next task.
Processor is so fast that it seems as though the tasks are done
simultaneously. Round robin system with each task allowed a small
amount of time. User can switch between programs. Different programs
available in different windows.
Single user OS
A single user OS allows one user at a time to use the system. It allocates
each user with rights and keeps the user files separate
Transparency
Actions which are taken by the operating system without the user being
aware of them.
Waterfall Method
Method of system lifecycle where each stage is fully completed before
moving onto the next stage.
Spiral Method
Where analysis, design and implementation are done together and
prototypes are produced by the programmer with the end user. This is
iterative development.
Feasibility Study
Looks at if creating a new system/software application is worthwhile.
Examines Technical, Social and Economic factors.
Information Gathering
Methods of finding out about current system. Questionnaire. Interviews.
Observation. Collection and analysis of documentation.
Installation Strategy
Parallel/pilot/phased/direct installation. Devise training program. Purchase
hardware. System must be tested with real data by end users. Write
technical and user documentation.
Software Maintenance
Corrective. Adaptive. Perfective.
User Guide/Documentation
Manual which explains how to use system. Contains FAQs. Installation
guide. Index. Glossary. Contents.
Technical Documentation
Written for future programmers. Contains Variable Names, Data Structure,
how the code works, Procedures names, DFDs, Flowcharts, Entity
Relationship Diagrams.
Play a video or music track whilst using a word
processor.
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Requirements Specification
List of requirements of the client for who the new system is being
produced. Consists of input, processing and output requirements. The
client agrees to these so no confusion when program is finished.
Design Specification
Taking the requirements specification and designing the stages to produce
the final system. Consists of input design (interface), output design, design
of data structure, any diagrams such as Flowcharts, DFDs, ERDs.
OCR
Characters shapes are scanned and these shapes are turned into text e.g.
scanning a printed page of text into a word processor document
OMR
Scanned page which reads the positions of marks on a document that are
made in a specific place which denotes inputted data. Multiple choice tests
or lottery tickets. Fast and accurate to process. Useful on multiple choice
tests as answers are all objective – no area for debate. Can be processed
in batches. Useful for partially sighted users to turn text into speech
synthesis.
Multiple Choice Test
MICR
Where special characters on document written using magnetisable ink
which are both computer and human readable.
Commonly used for printing account numbers on
used on banking cheques
Voice Recognition
Computer system can interpret spoken word into commands appropriate
for the application
Useful for partially sighted/sight deficient users
ALU
Carries out arithmetic instructions. Carries out logical instructions. Acts as
a gateway to processor.
Control Unit
Controls fetch/execute cycle. Manages execution of instructions by using
control signals to other parts of computer. Synchronises actions (using
inbuilt clock).
Memory Unit
Stores the OS/data currently in use and software currently in use
Program Counter
Stores the address of the next instruction and controls the sequence in
which the instructions are executed.
Memory Address Register
Stores the address in memory currently being accessed
Memory Data Register
Stores the data being transferred to or from memory
Current Instruction Register
Stores the instruction currently being executed
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Accumulator
Stores results of calculations performed
Data Bus
Transmit data between areas of the processor
Control Bus
Send control signals from control unit to other parts of the processor
Address Bus
Identification about where the data is being sent/coming from
Buffer
A small area of computer memory / temporary storage that holds data.
Interrupt
A signal or message sent to the processor that stops the current activity of
the processor.
Character Set
The symbols that may be represented by a computer. Normally equates to
the symbols on a keyboard. Each character on the keyboard has a binary
code which is unique. ASCII has 1 byte per character. Unicode has 2
bytes.
ASCII. Unicode
Verification
Checking input data with original data to ensure there have been no input
errors
Input same data twice and compare it
Validation
Validation ensures data meets certain rules. These are programmed in the
software.
Range Check
A number between a maximum and minimum range
>=1 and <=10
Format Check
A field may required letters and numbers in a certain order
Data entry for a NI number - LLNNNNNNL
(L)etter, (N)umber.
Presence Check
Checks data has been entered into a field.
Existence Check
Barcode is read at supermarket till. That number is looked up on a
database. If number is not on database then it must have been incorrectly
inputted.
Encoding
Shortening a data input for faster and easier entry.
Encryption
Scrambled data to make it illegible to someone. Can be decrypted by
using password. Helps make sensitive data more secure when
transmitting it.
(S)mall, (M)edium, (L)arge
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Backup
A backup is a copy of a file and its structure on a portable medium kept
away from originals so that if the original is corrupted it can be replaced.
Important files needs be protected from deliberate or accidental data loss.
Backup Strategy
Copy of files to backup medium – eg. Memory stick, CDRW, DVDRW (not
CD-Rom). Frequency of backup, Time backup is performed. Storage of
backup medium in safe location.
Archive
Data is put onto long term storage and kept offline so that it can be
referred to if necessary. Data is still available without taking up space on
working storage.
Disaster Recovery
Procedures that ensure data and systems can be restored following a
major disaster e.g. Fire in a building.
LAN
A local area network is a network covering a single building or site.
WAN
A WAN covers a wide geographical area crossing countries and
continents.
Handshake
The exchange of signals between devices to signify that they are ready for
communication. Rules/protocol will be agreed prior to the communication..
Without agreement on rules the two devices cannot understand each
other’s signals. One device may not be ready for communication eg may
be switched off
Router
Connects a LAN to a WAN
Protocol
A set of rules that governs communication between devices
Logical Protocol
The logical part of the protocol are things that are programmed in software
such as baud rate the error correction used, and any compression
techniques used.
Physical Protocol
The physical part of the protocol can be if data is transmitted wireless or
hard-wired, Serial or parallel or the type of cabling used e.g. copper wire,
or fibre optic, frequency of of wireless signal
Baud Rate
The speed in which data is transmitted between 2 devices or across a
LAN/WAN. Small bit rate required for downloading text document. High bit
rate required to watch video – time sensitive. Measured in bits per second.
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http
Hyper Text Transfer Protocol. Protocol which governs how web pages are
displayed over the internet.
Parallel Transmission
Multiple bits transmitted at a time down many wires eg. transferring data
from CPU to hard disk which has time sensitivity of data transfer.
Serial Transmission
One bit transmitted at a time down a single wire
Parity Bit
When using parity the total number of 1’s in a byte must be either an odd
or even number depending on the parity bit. This is the last bit in the byte.
Method of error detection.
Check Digit
A digit on the end of a string of numbers that has been calculated based
on an algorithm performed on the string of numbers. Used in error
checking.
Check Sum
Blocks of bytes are added before transmission to give a sum. The sum is
transmitted with the block. The same calculation is done on the data
blocks at the destination and result is compared with the transmitted value.
If different, there is a transmission error
Echoing
Data is transmitted. Received data is retransmitted back to sender. When
received at source returned signal is compared to original. If there are any
differences the data is retransmitted
Simplex
Communication in one direction only
Duplex
Communication in both directions simultaneously
Half Duplex
Communication in both directions but one at a time
NIC
Network Interface Card – Required to connect a PC to a network.
NOS
Network Operating System – OS required to manage the facilities of a
network/LAN.
Barcodes have a check digit to validate scanning.
ISBN – Mod 11.
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Packet Switching
Data split into packets sent onto network. Each packet finds the fastest
route to destination. Packets must be reordered at destination/arrives in
wrong order. Packets have identity on label. No established route for each
packet. Doesn’t tie up parts of network. Maximises use of network. Data
cannot be easily intercepted. Maximises use of network. Only as fast as its
slowest packet!
Circuit Switching
Route reserved before transmission. Establishes a route along which to
send data. Data sent down this route in its entirety. Can tie up large areas
of network.
Data Protection Act
Data protection Act governs the storage of personal data electronically. It
is required because
 Information is confidential and sensitive
 Information must be accurate
 Clients must have confidence that measures are taken to protect
their data
 Ensure irrelevant data is not kept
 Concerns about identity theft/fraud
 Stops data being passed onto 3rd parties for marketing purposes.
Computer Misuse Act
Law that governs unauthorised access to data - Hacking
Copyright Patents Act
Law that governs pirating software/music/images.
Last Updated : 10th March 2012 - Watford Boys Grammar School