541

GLOSSARY

Glossary

A* algorithm – an algorithm that finds the shortest route

between nodes or vertices but uses an additional heuristic

approach to achieve better performance than Dijkstra’s

algorithm.

Abnormal test data – test data that should be rejected by a program.

Absolute addressing – mode of addressing in which the

contents of the memory location in the operand are used.

Abstract data type (ADT) – a collection of data and a set of

operations on that data.

Abstraction – the process of extracting information that is

essential, while ignoring what is not relevant, for the

provision of a solution.

Acceptance testing – the testing of a completed program to

prove to the customer that it works as required.

Access rights (data security) – use of access levels to ensure

only authorised users can gain access to certain data.

Access rights (database) – the permissions given to database

users to access, modify or delete data.

Accumulator – temporary general purpose register which stores

numerical values at any part of a given operation.

Acknowledgement – message sent to a receiver to indicate that

data has been received without error.

ACM – Association for Computing Machinery.

Adaptive maintenance – the alteration of a program to perform

new tasks.

Address bus – carries the addresses throughout the computer

system.

Addressing modes – different methods of using the operand

part of a machine code instruction as a memory address.

Algorithm – an ordered set of steps to be followed in the

completion of a task.

Alpha testing – the testing of a completed or nearly completed

program in-house by the development team.

Analogue to digital converter (ADC) – needed to convert

analogue data (read from sensors, for example) into a form

understood by a computer.

Analysis – part of the program development lifecycle; a process

of investigation, leading to the specification of what a

program is required to do.

Anti-spyware software – software that detects and removes

spyware programs installed illegally on a user’s computer

system.

Antivirus software – software that quarantines and deletes files

or programs infected by a virus (or other malware); it can be

run in the background or initiated by the user.

Append – file access mode in which data can be added to the end

of a file.

Argument – the value passed to a procedure or function.

Arithmetic shift – the sign of the number is preserved.

Arithmetic-logic unit (ALU) – component in the processor

which carries out all arithmetic and logical operations.

ARPAnet – Advanced Research Projects Agency Network.

Array – a data structure containing several elements of the same

data type.

Artificial intelligence (AI) – machine or application which

carries out a task that requires some degree of intelligence

when carried out by a human counterpart.

Artificial neural networks – networks of interconnected nodes

based on the interconnections between neurons in the

human brain; the system is able to think like a human using

these neural networks, and its performance improves with

more data.

ASCII code – coding system for all the characters on a keyboard

and control codes.

Assembler – a computer program that translates programming

code written in assembly language into machine code;

assemblers can be one pass or two pass.

Assembly language – a low-level chip/machine specific

programming language that uses mnemonics.

Asymmetric encryption – encryption that uses public keys

(known to everyone) and private keys (secret keys).

Asynchronous serial data transmission – serial refers to a

single wire being used to transmit bits of data one after the

other; asynchronous refers to a sender using its own clock/

timer device rather sharing the same clock/timer with the

recipient device.

Attribute (database) – an individual data item stored for an

entity; for example, for a person, attributes could include

name, address, date of birth.

Attributes (class) – the data items in a class.

Audio compression – method used to reduce the size of a sound

file using perceptual music shaping.

Authentication – a way of proving somebody or something is

who or what they claim to be.

Automatic repeat request (ARQ) – a type of verification check.

Back propagation – method used in artificial neural networks

to calculate error gradients so that actual node/neuron

weightings can be adjusted to improve the performance of

the model.

Back-up utility – software that makes copies of files on another

portable storage device.

Backus-Naur form (BNF) notation – a formal method of

defining the grammatical rules of a programming language.

Bad sector – a faulty sector on an HDD which can be soft or

hard.

Base case – a terminating solution to a process that is not

recursive.

BCS – British Computer Society.

Belady’s anomaly – phenomenon which means it is possible to

have more page faults when increasing the number of page

frames.

Beta testing – the testing of a completed program by a small

group of users before it is released.

Bidirectional – used to describe a bus in which bits can travel

in both directions.

542

GLOSSARY

Big O notation – a mathematical notation used to describe the

performance or complexity of an algorithm.

Binary – base two number system based on the values 0 and 1 only.

Binary coded decimal (BCD) – number system that uses 4 bits

to represent each denary digit.

Binary file – a file that does not contain text only; the file is

machine-readable but not human-readable.

Binary floating-point number – a binary number written in the

form M × 2

(where M is the mantissa and E is the exponent).

Binary search – a method of searching an ordered list by testing

the value of the middle item in the list and rejecting the half

of the list that does not contain the required value.

Binary tree – a hierarchical data structure in which each parent

node can have a maximum of two child nodes.

Binder 3D printing – 3D printing method that uses a two-stage

pass; the first stage uses dry powder and the second stage

uses a binding agent.

Biometrics – use of unique human characteristics to identify a

user (such as fingerprints or face recognition).

BIOS – basic input/output system.

Birefringence – a reading problem with DVDs caused by

refraction of laser light into two beams.

Bit – abbreviation for binary digit.

Bit depth – number of bits used to represent the smallest unit

in, for example, a sound or image file; the larger the bit

depth, the better the quality of the sound or colour image.

Bit rate – number of bits per second that can be transmitted

over a network; it is a measure of the data transfer rate over

a digital telecoms network.

Bit streaming – contiguous sequence of digital bits sent over a

network/internet.

Bit-map image – system that uses pixels to make up an image.

BitTorrent – protocol used in peer-to-peer networks when

sharing files between peers.

Black-box testing – a method of testing a program that tests a

module’s inputs and outputs.

Block chaining – form of encryption, in which the previous

block of ciphertext is XORed with the block of plaintext and

then encrypted thus preventing identical plaintext blocks

producing identical ciphertext.

Block cipher – the encryption of a number of contiguous bits in

one go rather than one bit at a time.

Bluetooth – wireless connectivity that uses radio waves in the

2.45 GHz frequency band.

Boolean algebra – a form of algebra linked to logic circuits and

based on TRUE and FALSE.

Bootstrap – a small program that is used to load other programs

to ‘start up’ a computer.

Boundary test data – test data that is on the limit of that

accepted by a program or data that is just outside the limit

of that rejected by a program.

Breakpoint – a deliberate pause in the execution of a program

during testing so that the contents of variables, registers,

and so on can be inspected to aid debugging.

Bridge – device that connects LANs which use the same protocols.

Broadcast – communication where pieces of data are sent from

sender to receiver.

Bubble sort – a method of sorting data in an array into

alphabetical or numerical order by comparing adjacent items

and swapping them if they are in the wrong order.

Buffering – store which holds data temporarily.

Burst time – the time when a process has control of the CPU.

Bus network topology – network using single central cable in

which all devices are connected to this cable; data can only

travel in one direction and only one device is allowed to

transmit at a time.

By reference – a method of passing a parameter to a procedure

in which the value of the variable can be changed by the

procedure.

By value – a method of passing a parameter to a procedure in

which the value of the variable cannot be changed by the

procedure.

Cache memory – a high speed auxiliary memory which permits

high speed data transfer and retrieval.

Candidate key – an attribute or smallest set of attributes in a

table where no tuple has the same value.

Capacitive – type of touch screen technology based on glass

layers forming a capacitor; fingers touching the screen cause

a change in the electric field.

Certificate authority (CA) – commercial organisation used to

generate a digital certificate requested by website owners or

individuals.

Character set – a list of characters that have been defined by

computer hardware and software; it is necessary to have

a method of coding, so that the computer can understand

human characters.

Chatbot – computer program set up to simulate conversational

interaction between humans and a website.

Check digit – additional digit appended to a number to check if

entered data is error-free.

Checksum – verification method used to check if data

transferred has been altered or corrupted; calculated from

the block of data to be sent.

Ciphertext – the product when plaintext is put through an

encryption algorithm.

Circuit switching – method of transmission in which a dedicated

circuit/channel lasts throughout the duration of the

communication.

CISC – complex instruction set computer.

Class – a template defining the methods and data of a certain

type of object.

Classless inter-domain routing (CIDR) – increases IPv4

flexibility by adding a suffix to the IP address, such as

200.21.100.6/18.

CLI – command line interface.

Client-server – network that uses separate dedicated servers

and specific client work stations; all client computers are

connected to the dedicated servers.

Clock cycle – clock speeds are measured in terms of GHz; this is

the vibrational frequency of the clock which sends out pulses

along the control bus; a 3.5 GHZ clock cycle means 3.5 billion

clock cycles a second.

Close – file-processing operation; closes a file so it can no

longer be used by a program.

543

GLOSSARY

Cloud storage – method of data storage where data is stored on

off-site servers.

Cluster – a number of computers (containing SIMD processors)

networked together.

CMOS – complementary metal-oxide semiconductor.

Coaxial cable – cable made up of central copper core, insulation,

copper mesh and outer insulation.

Code generation – the third stage in the process of compilation;

this stage produces an object program.

Coding – part of the program development lifecycle; the writing

of the program or suite of programs.

Collision – situation in which two messages/data from different

sources are trying to transmit along the same data channel.

Colour depth – number of bits used to represent the colours in a

pixel, e.g. 8 bit colour depth can represent 2

= 256 Colours.

Combination circuit – circuit in which the output depends

entirely on the input values.

Compiler – a computer program that translates a source program

written in a high-level language to machine code or p-code,

object code.

Composite data type – a data type constructed using several of the

basic data types available in a particular programming language.

Composite key – a set of attributes that form a primary key to

provide a unique identifier for a table.

Conflict – situation in which two devices have the same IP address.

Constant – a named value that cannot change during the

execution of a program.

Constructor – a method used to initialise a new object.

Containment (aggregation) – process by which one class can

contain other classes.

Context switching – procedure by which, when the next process

takes control of the CPU, its previous state is reinstated or

restored.

Contiguous – items next to each other.

Control – to automatically take readings from a device, then use

the data from those readings to adjust the device.

Control bus – carries signals from control unit to all other

computer components.

Control unit – ensures synchronisation of data flow and

programs throughout the computer by sending out control

signals along the control bus.

Core – a unit made up of ALU, control unit and registers which is

part of a CPU; a CPU may contain a number of cores.

Corrective maintenance – the correction of any errors that

appear during use.

Cross-coupling – interconnection between two logic gates

which make up a flip-flop.

CSMA/CD – carrier sense multiple access with collision detection;

a method used to detect collisions and resolve the issue.

Culture – the attitudes, values and practices shared by a group

of people/society.

Current instruction register (CIR) – this is a register used to

contain the instruction which is currently being executed or

decoded.

Cyclic shift – no bits are lost; bits shifted out of one end of the

Data bus – allows data to be carried from processor to memory

(and vice versa) or to and from input/output devices.

Data definition language (DDL) – a language used to create,

modify and remove the data structures that form a database.

Data dictionary – a set of data that contains metadata (data

about other data) for a database.

Data hiding – technique which protects the integrity of an

object by restricting access to the data and methods within

that object.

Data integrity – the accuracy, completeness and consistency of

data.

Data management – the organisation and maintenance of data

in a database to provide the information required.

Data manipulation language (DML) – a language used to add,

modify, delete and retrieve the data stored in a relational

database.

Data modelling – the analysis and definition of the data

structures required in a database and to produce a data

model.

Data privacy – the privacy of personal information, or other

information stored on a computer, that should not be

accessed by unauthorised parties.

Data protection laws – laws which govern how data should be

kept private and secure.

Data redundancy – situation in which the same data is stored

on several servers in case of maintenance or repair.

Data security – methods taken to prevent unauthorised access

to data and to recover data if lost or corrupted.

Data type – a classification attributed to an item of data, which

determines the types of value it can take and how it can be

used.

Database – a structured collection of items of data that can be

accessed by different applications programs.

Database management system (DBMS) – systems software for

the definition, creation and manipulation of a database.

Debugging – the process of finding logic errors in a computer

program by running or tracing the program.

Declarative programming – statements of facts and rules

together with a mechanism for setting goals in the form of

a query.

Decomposition – the process of breaking a complex problem

into smaller parts.

Deep learning – machines that think in a way similar to the

human brain; they handle huge amounts of data using

artificial neural networks.

Design – part of the program development lifecycle; it uses the

program specification from the analysis stage to show how

the program should be developed.

Destructor – a method that is automatically invoked when an

object is destroyed.

Developer interface – feature of a DBMS that provides

developers with the commands required for definition,

creation and manipulation of a database.

Device driver – software that communicates with the operating

system and translates data into a format understood by the

device.

544

GLOSSARY

Dictionary – an abstract data type that consists of pairs, a key

and a value, in which the key is used to find the value.

Digest –a fixed-size numeric representation of the contents of

a message produced from a hashing algorithm; this can be

encrypted to form a digital signature.

Digital certificate – an electronic document used to prove the

identity of a website or individual; it contains a public key

and information identifying the website owner or individual;

issued by a CA.

Digital rights management (DRM) – used to control the access

to copyrighted material.

Digital signature – electronic way of validating the authenticity

of digital documents (that is, making sure they have not

been tampered with during transmission) and also proof that

a document was sent by a known user.

Digital to analogue converter (DAC) – needed to convert digital

data into electric currents that can drive motors, actuators

and relays, for example.

Dijkstra’s algorithm – an algorithm that finds the shortest path

between two nodes or vertices in a graph/network.

Direct 3D printing – 3D printing technique where print head

moves in the x, y and z directions. Layers of melted material

are built up using nozzles like an inkjet printer.

Direct access – a method of file access in which a record can be

physically found in a file without physically reading other

records.

Direct addressing – mode of addressing in which the contents

of the memory location in the operand are used; same as

absolute addressing.

Direct memory access (DMA) controller – device that allows

certain hardware to access RAM independently of the CPU.

Dirty – term used to describe a page in memory that has been

modified.

Disk compression – software that compresses data before

storage on an HDD.

Disk content analysis software – utility that checks disk drives

for empty space and disk usage by reviewing files and folders.

Disk defragmenter – utility that reorganises the sectors on

a hard disk so that files can be stored in contiguous data

blocks.

Disk formatter – utility that prepares a disk to allow data/files

to be stored and retrieved.

Disk thrashing – problem resulting from use of virtual memory;

excessive swapping in and out of virtual memory leads to

a high rate of hard disk read/write head movements thus

reducing processing speed.

DNS cache poisoning – altering IP addresses on a DNS server by

a ‘pharmer’ or hacker with the intention of redirecting a user

to their fake website.

Domain name service (DNS) – (also known as domain name

system) gives domain names for internet hosts and is a

system for finding IP addresses of a domain name.

Dry run – a method of testing a program that involves working

through a program or module from a program manually.

Dual core – a CPU containing two cores.

Dual layering – used in DVDs; uses two recording layers.

Dynamic link file (DLL) – a library routine that can be linked to

another program only at the run time stage.

Dynamic RAM (DRAM) – type of RAM chip that needs to be

constantly refreshed.

Eavesdropper – a person who intercepts data being transmitted.

Electronically erasable programmable read-only memory

(EEPROM)

– a read-only (ROM) chip that can be modified by

the user which can then be erased and written to repeatedly

using pulsed voltages.

Emulation – the use of an app/device to imitate the behaviour

of another program/device; for example, running an OS on a

computer which is not normally compatible.

Encapsulation – process of putting data and methods together

as a single unit, a class.

Encryption – the use of encryption keys to make data

meaningless without the correct decryption key.

Entity – anything that can have data stored about it; for

example, a person, place, event, thing.

Entity-relationship (E-R) model or E-R diagram – a graphical

representation of a database and the relationships between

the entities.

Enumerated data type – a non-composite data type defined by

a given list of all possible values that has an implied order.

Erasable PROM (EPROM) – type of ROM that can be programmed

more than once using ultraviolet (UV) light.

Ethernet – protocol IEEE 802.3 used by many wired LANs.

Ethical hacking – hacking used to test the security and

vulnerability of a computer system; the hacking is carried

out with the permission of the computer system owner, for

example, to help a company identify risks associated with

malicious hacking of their computer systems.

Ethics – moral principles governing an individual’s or

organisation’s behaviour, such as a code of conduct.

Even parity – binary number with an even number of 1-bits.

Exception – an unexpected event that disrupts the execution of

a program.

Exception handling – the process of responding to an exception

within the program so that the program does not halt

unexpectedly.

Exponent – the power of 2 that the mantissa (fractional part) is

raised to in a floating-point number.

Extreme test data – test data that is on the limit of that

accepted by a program.

Fact – a ‘thing’ that is known.

False positive – a file or program identified by a virus checker

as being infected but the user knows this cannot be correct.

Fetch-execute cycle – a cycle in which instructions and data are

fetched from memory and then decoded and finally executed.

Fibre optic cable – cable made up of glass fibre wires which use

pulses of light (rather than electricity) to transmit data.

Field – a column in a table in a database.

File – a collection of data stored by a computer program to be

used again.

File access – the method used to physically find a record in the

file.

File organisation – the way that records of data are physically

stored in a file, including the structure and ordering of the

records.

545

GLOSSARY

File server – a server on a network where central files and other

data are stored; they can be accessed by a user logged onto

the network.

Finite state machine (FSM) – a mathematical model of a

machine that can be in one state of a fixed set of possible

states; one state is changed to another by an external input;

this is known as a transition.

Firewall – software or hardware that sits between a computer

and external network which monitors and filters all incoming

and outgoing activities.

First in first out (FIFO) page replacement – page replacement

that keeps track of all pages in memory using a queue

structure; the oldest page is at the front of the queue and is

the first to be removed when a new page is added.

First normal form (1NF) – the status of a relational database in

which entities do not contain repeated groups of attributes.

Flag – indicates the status of a bit in the status register; for

example, N = 1 indicates the result of an addition gives a

negative value.

Flash memory – a type of EEPROM, particularly suited to use in

drives such as SSDs, memory cards and memory sticks.

Flip-flop circuits – electronic circuits with two stable

conditions using sequential circuits.

Flowchart – a diagrammatic representation of an algorithm.

Foreign key – a set of attributes in one table that refer to the

primary key in another table.

Fragmented – storage of data in non-consecutive sectors; for

example, due to editing and deletion of old data.

Frame rate – number of video frames that make up a video per

second.

Frames – fixed-size physical memory blocks.

Free Software Foundation – organisation promoting the free

distribution of software, giving users the freedom to run,

copy, change or adapt the coding as needed.

Freeware – software that can be downloaded free of charge;

however, it is covered by the usual copyright laws and cannot

be modified; nor can the code be used for another purpose.

FTP –file transfer protocol.

Full adder circuit – two half adders combined to allow the sum

of several binary bits.

Function – a set of statements that can be grouped together

and easily called in a program whenever required, rather

than repeating all of the statements each time. Unlike a

procedure, a function always returns a value.

Gateway – device that connects LANs which use different

protocols.

General case – a solution to a process that is recursively defined.

Getter – a method that gets the value of a property.

Graph – a non-linear data structure consisting of nodes and edges.

Gray codes – ordering of binary numbers such that successive

numbers differ by one bit value only, for example, 00 01 11 10.

Guest OS – an OS running on a virtual machine.

GUI – graphical user interface.

Hacking – illegal access to a computer system without the

owner’s permission.

Half adder circuit – carries out binary addition on two bits

giving sum and carry.

Handshake – the process of initiating communication between

two devices; this is initiated by one device sending a

message to another device requesting the exchange of data.

Hard disk drive (HDD) – type of magnetic storage device that

uses spinning disks.

Hardware management – part of the operating system that

controls all input/output devices connected to a computer

(made up of sub-management systems such as printer

management, secondary storage management, and so on).

Hashing algorithm (cryptography) – a function which

converts a data string into a numeric string which is used in

cryptography.

Hashing algorithm (file access) – a mathematical formula used

to perform a calculation on the key field of the record; the

result of the calculation gives the address where the record

should be found.

HCI – human–computer interface.

Header (procedure or function) – the first statement in the

definition of a procedure or function, which contains its

name, any parameters passed to it, and, for a function, the

type of the return value.

Header (data packet) – part of a data packet containing key

data such as destination IP address, sequence number, and

so on.

Heuristic – method that employs a practical solution (rather

than a theoretical one) to a problem; when applied to

algorithms this includes running tests and obtaining results

by trial and error.

Heuristic checking – checking of software for behaviour that

could indicate a possible virus.

Hexadecimal – a number system based on the value 16 (uses the

denary digits 0 to 9 and the letters A to F).

High-bandwidth digital copy protection (HDCP) – part of HDMI

technology which reduces risk of piracy of software and

multimedia.

High-definition multimedia interface (HDMI) – type of port

connecting devices to a computer.

Hop number/hopping – number in the packet header used

to stop packets which never reach their destination from

‘clogging up’ routes.

Host – a computer or device that can communicate with other

computers or devices on a network.

Host OS – an OS that controls the physical hardware.

Host-to-host – a protocol used by TCP when communicating

between two devices.

HTTP – hypertext transfer protocol.

Hub – hardware used to connect together a number of devices to

form a LAN; directs incoming data packets to all devices on

the network (LAN).

Hybrid network – network made up of a combination of other

network topologies.

HyperText Mark-up Language (HTML) – used to design web

pages and to write http(s) protocols, for example.

Hypervisor – virtual machine software that creates and runs

virtual machines.

Icon – small picture or symbol used to represent, for example, an

application on a screen.

Identifier – a unique name applied to an item of data.

546

GLOSSARY

IEEE – Institute of Electrical and Electronics Engineers.

Image resolution – number of pixels that make up an image;

for example, an image could contain 4096 × 3192 pixels

(13 074 432 pixels in total).

IMAP – internet message access protocol.

Immediate access store (IAS) – holds all data and programs

needed to be accessed by the control unit.

Immediate addressing – mode of addressing in which the value

of the operand only is used.

Imperative programming – programming paradigm in which the

steps required to execute a program are set out in the order

they need to be carried out.

In demand paging – a form of data swapping where pages of

data are not copied from HDD/SSD into RAM until they are

actually required.

Index (database) – a data structure built from one or more

columns in a database table to speed up searching for data.

Index (array) – a numerical indicator of an item of data’s

position in an array.

Indexed addressing – mode of addressing in which the contents

of the memory location found by adding the contents of the

index register (IR) to the address of the memory location in

the operand are used.

Indirect addressing – mode of addressing in which the contents

of the contents of the memory location in the operand are

used.

Inheritance – process in which the methods and data from one

class, a superclass or base class, are copied to another class,

a derived class.

Insertion sort – a method of sorting data in an array into

alphabetical or numerical order by placing each item in turn

in the correct position in the sorted list.

Instance – An occurrence of an object during the execution of a

program.

Instruction – a single operation performed by a CPU.

Instruction set – the complete set of machine code instructions

used by a CPU.

Integrated development environment (IDE) – a suite of

programs used to write and test a computer program written

in a high-level programming language.

Integration testing – a method of testing a program that tests

combinations of program modules that work together.

Intellectual property rights – rules governing an individual’s

ownership of their own creations or ideas, prohibiting the

copying of, for example, software without the owner’s

permission.

Internet – massive network of networks, made up of computers

and other electronic devices; uses TCP/IP communication

protocols.

Internet protocol (IP) – uses IPv4 or IPv6 to give addresses to

devices connected to the internet.

Internet service provider (ISP) – company which allows a user

to connect to the internet; they will usually charge a monthly

fee for the service they provide.

Interpreter – a computer program that analyses and executes a

program written in a high-level language line by line.

Interrupt – signal sent from a device or software to a processor

requesting its attention; the processor suspends all

operations until the interrupt has been serviced.

Interrupt dispatch table (IDT) – data structure used to

implement an interrupt vector table.

Interrupt priority – all interrupts are given a priority so that

the processor knows which need to be serviced first and

which interrupts are to be dealt with quickly.

Interrupt priority levels (IPL) – values given to interrupts

based on values 0 to 31.

Interrupt service routine (ISR) or interrupt handler – software

which handles interrupt requests (such as ‘printer out of

paper’) and sends the request to the CPU for processing.

IPv4 – IP address format which uses 32 bits, such as 200.21.100.6.

IPv6 – newer IP address format which uses 128 bits, such as

A8F0:7FFF:F0F1:F000:3DD0: 256A:22FF:AA00.

Iterative model – a type of program development cycle in which

a simple subset of the requirements is developed, then

expanded or enhanced, with the development cycle being

repeated until the full system has been developed.

JavaScript – object-orientated (or scripting) programming

language used mainly on the web; used to enhance HTML

pages.

JPEG – Joint Photographic Expert Group; a form of lossy file

compression based on the inability of the eye to spot certain

colour changes and hues.

Karnaugh maps (K-maps) – a method used to simplify logic

statements and logic circuits; uses Gray codes.

Kernel – the core of an OS with control over process

management, memory management, interrupt handling,

device management and I/O operations.

Key distribution problem – security issue inherent in symmetric

encryption arising from the fact that, when sending the

secret key to a recipient, there is the risk that the key can be

intercepted by an eavesdropper/hacker.

Labelled data – data where we know the target answer and the

data object is fully recognised.

LAN – local area network (network covering a small area such as

a single building).

Latency – the lag in a system; for example, the time to find a

track on a hard disk, which depends on the time taken for the

disk to rotate around to its read-write head.

Least recently used (LRU) page replacement – page

replacement algorithm in which the page which has not been

used for the longest time is replaced.

Leech – a peer with negative feedback from swarm members.

Left shift – bits are shifted to the left.

Legal – relating to, or permissible by, law.

Lexical analysis – the first stage in the process of compilation;

removes unnecessary characters and tokenises the program.

Library program – a program stored in a library for future use by

other programmers.

Library routine – a tested and ready-to-use routine available in

the development system of a programming language that can

be incorporated into a program.

Linear search – a method of searching in which each element of

an array is checked in order.

547

GLOSSARY

Linked list – a list containing several items in which each item

in the list points to the next item in the list.

Logic circuit – formed from a combination of logic gates and

designed to carry out a particular task; the output from a

logic circuit will be 0 or 1.

Logic error – an error in the logic of a program.

Logic gates – electronic circuits which rely on ‘on/off’ logic; the

most common ones are NOT, AND, OR, NAND, NOR and XOR.

Logical memory – the address space that an OS perceives to be

main storage.

Logical schema – a data model for a specific database that is

independent of the DBMS used to build that database.

Logical shift – bits shifted out of the register are replaced with

zeros.

Lossless file compression – file compression method where the

original file can be restored following decompression.

Lossy file compression – file compression method where

parts of the original file cannot be recovered during

decompression; some of the original detail is lost.

Low level scheduling – method by which a system assigns a

processor to a task or process based on the priority level.

Lower bound – the index of the first element in an array, usually

0 or 1.

Low-level programming – programming instructions that use

the computer’s basic instruction set.

Lurker – user/client that downloads files but does not supply

any new content to the community.

Machine code – the programming language that the CPU uses.

Machine learning – systems that learn without being

programmed to learn.

Maintenance – part of the program development lifecycle; the

process of making sure that the program continues to work

during use.

Malicious hacking – hacking done with the sole intent of

causing harm to a computer system or user (for example,

deletion of files or use of private data to the hacker’s

advantage).

Malware – malicious software that seeks to damage or gain

unauthorised access to a computer system.

MAN – metropolitan area network (network which is larger than

a LAN but smaller than a WAN; can cover several buildings in

a single city, such as a university campus).

Mantissa – the fractional part of a floating point number.

Mask – a number that is used with the logical operators AND, OR

or XOR to identify, remove or set a single bit or group of bits

in an address or register.

Massively parallel computers – the linking together of several

computers effectively forming one machine with thousands

of processors.

Memory cache – high speed memory external to processor which

stores data which the processor will need again.

Memory dump – contents of a computer memory output to

screen or printer.

Memory management – part of the operating system that

controls the main memory.

Memory optimisation – function of memory management that

determines how memory is allocated and deallocated.

Memory organisation – function of memory management that

determines how much memory is allocated to an application.

Memory protection – function of memory management that

ensures two competing applications cannot use same memory

locations at the same time.

Mesh network topology – interlinked computers/devices,

which use routing logic so data packets are sent from

sending stations to receiving stations only by the shortest

route.

Metadata – a set of data that describes and gives information

about other data.

Method – a programmed procedure that is defined as part of a

class.

MIMD – multiple instruction multiple data, computer

architecture which uses many processors, each of which can

use a separate data source.

MIME – multi-purpose internet mail extension; a protocol that

allows email attachments containing media files as well as

text to be sent.

MISD – multiple instruction single data, computer architecture

which uses many processors but the same shared data source.

Modem – modulator demodulator; device which converts digital

data to analogue data (to be sent down a telephone wire);

conversely it also converts analogue data to digital data

(which a computer can process).

Modulo-11 – method used to calculate a check digit based on

modulus division by 11.

Monitor – to automatically take readings from a device.

Morality – an understanding of the difference between right and

wrong, often founded in personal beliefs.

MP3/MP4 files – file compression method used for music and

multimedia files.

Multitasking – function allowing a computer to process more

than one task/process at a time.

NIC – network interface card; these cards allow devices to

connect to a network/internet (usually associated with a

MAC address set at the factory).

Node – device connected to a network (it can be a computer,

storage device or peripheral device).

Node or vertex – fundamental unit from which graphs are

formed (nodes and vertices are the points where edges

converge).

Non-composite data type – a data type that does not reference

any other data types.

Non-preemptive – type of scheduling in which a process

terminates or switches from a running state to a waiting state.

Normal test data – test data that should be accepted by a

program.

Normalisation (database) – the process of organising data

to be stored in a database into two or more tables and

relationships between the tables, so that data redundancy is

minimised.

Normalisation (floating-point) – a method to improve the

precision of binary floating-point numbers; positive numbers

should be in the format 0.1 and negative numbers in the

format 1.0.

Object – an instance of a class that is self-contained and

includes data and methods.

548

GLOSSARY

Object code – a computer program after translation into machine

code.

Object-oriented programming (OOP) – a programming

methodology that uses self-contained objects, which contain

programming statements (methods) and data, and which

communicate with each other.

Odd parity – binary number with an odd number of 1-bits.

On demand (bit streaming) – system that allows users to

stream video or music files from a central server as and

when required without having to save the files on their own

computer/tablet/phone.

One’s complement – each binary digit in a number is reversed to

allow both negative and positive numbers to be represented.

Opcode – short for operation code, the part of a machine code

instruction that identifies the action the CPU will perform.

Open – file-processing operation; opens a file ready to be used

in a program.

Open Source Initiative – organisation offering the same

freedoms as the Free Software Foundation, but with more

of a focus on the practical consequences of the four shared

rules, such as more collaborative software development.

Operand – the part of a machine code instruction that identifies

the data to be used by the CPU.

Operating system – software that provides an environment

in which applications can run and provides an interface

between hardware and human operators.

Optical storage – CDs, DVDs and Blu-ray® discs that use laser

light to read and write data.

Optimal page replacement – page replacement algorithm that

looks forward in time to see which frame to replace in the

event of a page fault.

Optimisation (compilation) – the fourth stage in the process of

compilation; the creation of an efficient object program.

Optimisation (memory management) – function of memory

management deciding which processes should be in main

memory and where they should be stored.

Organic LED (OLED) – uses movement of electrons between

cathode and anode to produce an on-screen image; generates

its own light so no back lighting required.

Overclocking – changing the clock speed of a system clock to a

value higher than the factory/recommended setting.

Overflow – the result of carrying out a calculation which produces

a value too large for the computer’s allocated word size.

Overloading – feature of object-oriented programming that

allows a method to be defined more than once in a class, so

it can be used in different situations.

Packet – a message/data is split up into smaller groups of bits

for transmission over a network.

Packet switching – method of transmission where a message

is broken into packets which can be sent along paths

independently from each other.

Page fault – occurs when a new page is referred but is not yet in

memory.

Page replacement – occurs when a requested page is not in

memory and a free page cannot be used to satisfy allocation.

Page table – table that maps logical addresses to physical

addresses; it contains page number, flag status, frame

address and time of entry.

Pages – fixed-size logical memory blocks.

Paging – form of memory management which divides up physical

memory and logical memory into fixed-size memory blocks.

PAN – network that is centred around a person or their

workspace.

Parallel processing – operation which allows a process to be

split up and for each part to be executed by a different

processor at the same time.

Parameter – a variable applied to a procedure or function that

allows one to pass in a value for the procedure to use.

Parity bit – an extra bit found at the end of a byte that is set

to 1 if the parity of the byte needs to change to agree with

sender/receiver parity protocol.

Parity block – horizontal and vertical parity check on a block of

data being transferred.

Parity byte – additional byte sent with transmitted data to

enable vertical parity checking (as well as horizontal parity

checking) to be carried out.

Parity check – method used to check if data has been

transferred correctly; uses even or odd parity.

Pattern recognition – the identification of parts of a problem

that are similar and could use the same solution.

Peer – a client who is part of a peer-to-peer network/file sharing

community.

Peer-to-peer – network in which each node can share its files

with all the other nodes; each node has its own data; there is

no central server.

Perceptual music shaping – method where sounds outside

the normal range of hearing of humans, for example, are

eliminated from the music file during compression.

Perfective maintenance – the process of making improvements

to the performance of a program.

Pharming – redirecting a user to a fake website in order to

illegally obtain personal data about the user.

Phishing – legitimate-looking emails designed to trick a

recipient into giving their personal data to the sender of the

email.

PHP – hypertext processor; an HTML-embedded scripting

language used to write web pages.

Physical memory – main/primary RAM memory.

Pieces – splitting up of a file when using peer-to-peer file

sharing.

Pinching and rotating – actions by fingers on a touch screen to

carry out tasks such as move, enlarge, reduce, and so on.

Pipelining – allows several instructions to be processed

simultaneously without having to wait for previous

instructions to finish.

Piracy – the practice of using or making illegal copies of, for

example, software.

Pixel – smallest picture element that makes up an image.

Pixel density – number of pixels per square centimetre.

Plagiarism – the act of taking another person’s work and

claiming it as one’s own.

Plaintext – the original text/document/message before it is put

through an encryption algorithm.

Pointer data type – a non-composite data type that uses the

memory address of where the data is stored.

549

GLOSSARY

Polymorphism – feature of object-oriented programming that

allows methods to be redefined for derived classes.

POP – post office protocol.

Port – external connection to a computer which allows it to

communicate with various peripheral devices; a number of

different port technologies exist.

Positive feedback – the output from a process which influences

the next input value to the process.

Post-WIMP – interfaces that go beyond WIMP and use touch

screen technology rather than a pointing device.

Preemptive – type of scheduling in which a process switches

from running state to steady state or from waiting state to

steady state.

Prettyprinting – the practice of displaying or printing well set

out and formatted source code, making it easier to read and

understand.

Primary key – a unique identifier for a table, it is a special case

of a candidate key.

Privacy – the right to keep personal information and data

secret, and for it to not be unwillingly accessed or shared

through, for example, hacking.

Private IP address – an IP address reserved for internal network

use behind a router.

Private key – encryption/decryption key which is known only to

a single user/computer.

Procedure – a set of statements that can be grouped together

and easily called in a program whenever required, rather than

repeating all of the statements each time.

Process – a program that has started to be executed.

Process control block (PCB) – data structure which contains all

the data needed for a process to run.

Process management – part of the operating system that

involves allocation of resources and permits the sharing and

exchange of data.

Process states – running, ready and blocked; the states of a

process requiring execution.

Product key – security method used in software to protect

against illegal copies or use.

Program counter (PC) – a register used in a computer to store

the address of the instruction which is currently being

executed.

Program development lifecycle – the process of developing

a program set out in five stages: analysis, design, coding,

testing and maintenance.

Program library – a library on a computer where programs and

routines are stored which can be freely accessed by other

software developers for use in their own programs.

Programmable ROM (PROM) – type of ROM chip that can be

programmed once.

Programming paradigm – a set of programming concepts.

Property – data and methods within an object that perform a

named action.

Protocol – a set of rules governing communication across a

network; the rules are agreed by both sender and recipient.

Pseudocode – a method of showing the detailed logical steps in

an algorithm, using keywords, identifiers with meaningful

names, and mathematical operators.

Public IP address – an IP address allocated by the user’s ISP to

identify the location of their device on the internet.

Public key – encryption/decryption key known to all users.

Public key infrastructure (PKI) – a set of protocols, standards

and services that allow users to authenticate each other

using digital certificates issued by a CA.

Public switched telephone network (PSTN) – network used by

traditional telephones when making calls or when sending

faxes.

Pull protocol – protocol used when receiving emails, in which

the client periodically connects to a server, checks for and

downloads new emails from a server and then closes the

connection.

Push protocol – protocol used when sending emails, in which

the client opens the connection to the server and keeps the

connection active all the time, then uploads new emails to

the server.

Quad core – a CPU containing four cores.

Quantum – a fixed time slice allocated to a process.

Quantum cryptography – cryptography based on the laws of

quantum mechanics (the properties of photons).

Quantum key distribution (QKD) – protocol which uses

quantum mechanics to securely send encryption keys over

fibre optic networks.

Quarantine – file or program identified as being infected by a

virus which has been isolated by antivirus software before it

is deleted at a later stage.

Qubit – the basic unit of a quantum of information (quantum bit).

Query processor – feature of a DBMS that processes and

executes queries written in structured query language (SQL).

Queue – a list containing several items operating on the first in,

first out (FIFO) principle.

Random access memory (RAM) – primary memory unit that can

be written to and read from.

Random file organisation – a method of file organisation in which

records of data are physically stored in a file in any available

position; the location of any record in the file is found by

using a hashing algorithm on the key field of a record.

Rapid application development (RAD) – a type of program

development cycle in which different parts of the

requirements are developed in parallel, using prototyping to

provide early user involvement in testing.

Read – file access mode in which data can be read from a file.

Read-only memory (ROM) – primary memory unit that can only

be read from.

Real-time (bit streaming) – system in which an event is

captured by camera (and microphone) connected to a

computer and sent to a server where the data is encoded; the

user can access the data ‘as it happens’ live.

Record (database) – a row in a table in a database.

Record (data type) – a composite data type comprising several

related items that may be of different data types.

Recursion – a process using a function or procedure that is

defined in terms of itself and calls itself.

Referential integrity – property of a database that does not

contain any values of a foreign key that are not matched to

the corresponding primary key.

550

GLOSSARY

Refreshed – requirement to charge a component to retain its

electronic state.

general or specific in its use; holds data or instructions as

part of the fetch-execute cycle.

show movement of data and instructions in a processor, can

be used to represent the operation of the fetch-execute

cycle.

Regression – statistical measure used to make predictions from

data by finding learning relationships between the inputs

and outputs.

Reinforcement learning – system which is given no training;

learns on basis of ‘reward and punishment’.

Relational database – a database where the data items are

linked by internal pointers.

Relationship – situation in which one table in a database has a

foreign key that refers to a primary key in another table in

the database.

Relative addressing – mode of addressing in which the memory

address used is the current memory address added to the

operand.

Removable hard disk drive – portable hard disk drive that is

external to the computer; it can be connected via a USB port

when required; often used as a device to back up files and

data.

Repeater – device used to boost a signal on both wired and

wireless networks.

Repeating hubs – network devices which are a hybrid of hub and

repeater unit.

Report window – a separate window in the runtime environment

of the IDE that shows the contents of variables during the

execution of a program.

Resistive – type of touch screen technology; when a finger

touches the screen, the glass layer touches the plastic layer,

completing the circuit and causing a current to flow at that

point.

Resolution – number of pixels per column and per row on a

monitor or television screen.

Reverse Polish notation (RPN) – a method of representing

an arithmetical expression without the use of brackets or

special punctuation.

Reward and punishment – improvements to a model based

on whether feedback is positive or negative; actions are

optimised to receive an increase in positive feedback.

Right shift – bits are shifted to the right.

RISC – reduced instruction set computer.

Round robin (scheduling) – scheduling algorithm that uses time

slices assigned to each process in a job queue.

Router – device which enables data packets to be routed

between different networks (for example, can join LANs to

form a WAN).

Routing table – a data table that contains the information

necessary to forward a package along the shortest or best

route to allow it to reach its destination.

Rules – relationships between facts.

Run length encoding (RLE) – a lossless file compression

technique used to reduce text and photo files in particular.

Run-time error – an error found in a program when it is

executed; the program may halt unexpectedly.

Sampling rate – number of sound samples taken per second.

Sampling resolution/bit depth – number of bits used to

represent sound amplitude.

Scheduling – process manager which handles the removal of

running programs from the CPU and the selection of new

processes.

Screen resolution – number of horizontal and vertical pixels

that make up a screen display; if the screen resolution is

smaller than the image resolution, the whole image cannot

be shown on the screen, or the original image will become

lower quality.

Second normal form (2NF) – the status of a relational database

in which entities are in 1NF and any non-key attributes

depend upon the primary key.

Secondary key – a candidate key that is an alternative to the

primary key.

Secure Sockets Layer (SSL) – security protocol used when

sending data over the internet.

Security management – part of the operating system that

ensures the integrity, confidentiality and availability of data.

Seed – a peer that has downloaded a file (or pieces of a file) and

has then made it available to other peers in the swarm.

Segment (transport layer) – this is a unit of data (packet)

associated with the transport layer protocols.

Segment map table – table containing the segment number,

segment size and corresponding memory location in physical

memory; it maps logical memory segments to physical memory.

Segment number – index number of a segment.

Segments (memory) – variable-size memory blocks into which

logical memory is split up.

Semi-supervised (active) learning – system that interactively

queries source data to reach the desired result; it uses both

labelled and unlabelled data, but mainly unlabelled data on

cost grounds.

Sensor – input device that reads physical data from its

surroundings.

Sequential access – a method of file access in which records are

searched one after another from the physical start of the file

until the required record is found.

Sequential circuit – circuit in which the output depends on

input values produced from previous output values.

Sequential file organisation – a method of file organisation in

which records of data are physically stored in a file, one after

another, in a given order.

Serial access – a method of file access in which records are

searched one after another from the physical start of the file

until the required record is found.

Serial file organisation – a method of file organisation in which

records of data are physically stored in a file, one after

another, in the order they were added to the file.

Session caching – function in TLS that allows a previous

computer session to be ‘remembered’, therefore preventing

the need to establish a new link each time a new session is

attempted.

Set – a given list of unordered elements that can use set theory

operations such as intersection and union.

551

GLOSSARY

Setter – a method used to control changes to a variable.

Shareware – software that is free of charge initially (free

trial period); the full version of the software can only be

downloaded once the full fee for the software has been paid.

Shift – moving the bits stored in a register a given number of

places within the register; there are different types of shift.

Sign and magnitude – binary number system where left-most bit

is used to represent the sign (0 = + and 1 = –); the remaining

bits represent the binary value.

SIMD – single instruction multiple data, computer architecture

which uses many processors and different data inputs.

Single stepping – the practice of running a program one line/

instruction at a time.

SISD – single instruction single data, computer architecture

which uses a single processor and one data source.

SMTP – simple mail transfer protocol.

Softmodem – abbreviation for software modem; a software-

based modem that uses minimal hardware.

Solid state drive (SSD) – storage media with no moving parts

that relies on movement of electrons.

Source code – a computer program before translation into

machine code.

Spread spectrum frequency hopping – a method of transmitting

radio signals in which a device picks one of 79 channels at

random. If the chosen channel is already in use, it randomly

chooses another channel. It has a range up to 100 metres.

Spread spectrum technology – wideband radio frequency with a

range of 30 to 50 metres.

SQL script – a list of SQL commands that perform a given task,

often stored in a file for reuse.

Stack – a list containing several items operating on the last in,

first out (LIFO) principle.

Star network topology – a network that uses a central hub/

switch with all devices connected to this central hub/switch;

all data packets are directed through this central hub/switch.

Starve – to constantly deprive a process of the necessary

resources to carry out a task/process.

State-transition diagram – a diagram showing the behaviour of

a finite state machine (FSM).

State-transition table – a table showing every state of a finite

state machine (FSM), each possible input and the state after

the input.

Static RAM (SRAM) – type of RAM chip that uses flip-flops and

does not need refreshing.

Status register – used when an instruction requires some form

of arithmetic or logical processing.

Stepwise refinement – the practice of subdividing each part of

a larger problem into a series of smaller parts, and so on, as

required.

Stream cipher – the encryption of bits in sequence as they

arrive at the encryption algorithm.

Structure chart – a modelling tool used to decompose a problem

into a set of sub-tasks. It shows the hierarchy or structure

of the different modules and how they connect and interact

with each other.

Structured English – a method of showing the logical steps

in an algorithm, using an agreed subset of straightforward

English words for commands and mathematical operations.

Structured query language (SQL) – the standard query

language used with relational databases for data definition

and data modification.

State-transition table – a table showing every state of a finite

state machine (FSM), each possible input and the state after

the input.

Stub testing – the use of dummy modules for testing purposes.

Sub-netting – practice of dividing networks into two or more

sub-networks.

Sum of products (SoP) – a Boolean expression containing AND

and OR terms.

Super computer – a powerful mainframe computer.

Supervised learning – system which is able to predict future

outcomes based on past data; it requires both input and

output values to be used in the training process.

Swap space – space on HDD used in virtual memory, which saves

process data.

Swarm – connected peers (clients) that share a torrent/tracker.

Switch – hardware used to connect together a number of devices

to form a LAN; directs incoming data packets to a specific

destination address only.

Symbolic addressing – mode of addressing used in assembly

language programming; a label is used instead of a value.

Symmetric encryption – encryption in which the same secret

key is used to encrypt and decrypt messages.

Syntax analysis – the second stage in the process of

compilation; output from the lexical analysis is checked for

grammatical (syntax) errors.

Syntax diagram – a graphical method of defining and showing

the grammatical rules of a programming language.

Syntax error – an error in the grammar of a source program.

System clock – produces timing signals on the control bus to

ensure synchronisation takes place.

Table – a group of similar data, in a database, with rows for each

instance of an entity and columns for each attribute.

TCP – transmission control protocol.

Test plan – a detailed list showing all the stages of testing and

every test that will be performed for a particular program.

Test strategy – an overview of the testing required to meet the

requirements specified for a particular program; it shows how

and when the program is to be tested.

Testing – part of the program development lifecycle; the

testing of the program to make sure that it works under all

conditions.

Thick client – device which can work both off line and on line

and is able to do some processing even if not connected to a

network/internet.

Thin client – device that needs access to the internet for

it to work; it depends on a more powerful computer for

processing.

Third normal form (3NF) – the status of a relational database

in which entities are in 2NF and all non-key attributes are

independent.

Thrash point – point at which the execution of a process comes

to a halt since the system is busier paging in/out of memory

rather than actually executing them.

Timeout – time allowed to elapse before an acknowledgement is

received.

552

GLOSSARY

Touch screen – screen on which the touch of a finger or stylus

allows selection or manipulation of a screen image; they

usually use capacitive or resistive technology.

Trace table – a table showing the process of dry-running a

program with columns showing the values of each variable as

it changes.

Tracker – central server that stores details of all other computers

in the swarm.

Translation lookaside buffer (TLB) – this is a memory cache

which can reduce the time taken to access a user memory

location; it is part of the memory management unit.

Translator – the systems software used to translate a source

program written in any language other than machine code.

Transport Layer Security (TLS) – a more up-to-date version of SSL.

Truth table – a method of checking the output from a logic

circuit; they use all the possible binary input combinations

depending on the number of inputs; for example, 2 inputs

have 2

(4) possible binary combinations, 3 inputs will have

(8) possible binary combinations, and so on.

Tuple – one instance of an entity, which is represented by a row

in a table.

Twisted pair cable – type of cable in which two wires of a single

circuit are twisted together; several twisted pairs make up a

single cable.

Two’s complement – each binary digit is reversed and 1 is

added in right-most position to produce another method of

representing positive and negative numbers.

Underflow – the result of carrying out a calculation which produces

a value too small for the computer’s allocated word size.

Unicode – coding system which represents all the languages of

the world (first 128 characters are the same as ASCII code).

Unidirectional – used to describe a bus in which bits can travel

in one direction only.

Uniform resource locator (URL) – specifies location of a web

page (for example, www.hoddereducation.co.uk).

Universal Serial Bus (USB) – a type of port connecting devices

to a computer.

Unlabelled data – data where objects are undefined and need to

be manually recognised.

Unsupervised learning – system which is able to identify hidden

patterns from input data; the system is not trained on the

‘right’ answer.

Unwinding – process which occurs when a recursive function

finds the base case and the function returns the values.

Upper bound – the index of the last element in an array.

User account – an agreement that allows an individual to use a

computer or network server, often requiring a user name and

password.

User defined data type – a data type based on an existing

data type or other data types that have been defined by a

programmer.

Utility program – parts of the operating system which carry out

certain functions, such as virus checking, defragmentation or

hard disk formatting.

Validation – method used to ensure entered data is reasonable

and meets certain input criteria.

Variable – a named value that can change during the execution

of a program.

Vector graphics – images that use 2D points to describe lines

and curves and their properties that are grouped to form

geometric shapes.

Verification – method used to ensure data is correct by using

double entry or visual checks.

Video Graphics Array (VGA) – type of port connecting devices

to a computer.

Virtual machine – an emulation of an existing computer system;

a computer OS running within another computer’s OS.

Virtual memory – type of paging that gives the illusion of

unlimited memory being available.

Virtual memory systems – memory management (part of OS) that

makes use of hardware and software to enable a computer to

compensate for shortage of actual physical memory.

Virtual reality headset – apparatus worn on the head that

covers the eyes like a pair of goggles; it gives the user the

‘feeling of being there’ by immersing them totally in the

virtual reality experience.

Voice over Internet Protocol (VoIP) – converts voice and webcam

images into digital packages to be sent over the internet.

Von Neumann architecture – computer architecture which

introduced the concept of the stored program in the 1940s.

Walkthrough – a method of testing a program; a formal version

of a dry run using pre-defined test cases.

WAN – wide area network (network covering a very large

geographical area).

(W)AP – (wireless) access point which allows a device to access

a LAN without a wired connection.

Waterfall model – a linear sequential program development cycle,

in which each stage is completed before the next is begun.

Web browser – software that connects to DNS to locate IP

addresses; interprets web pages sent to a user’s computer so that

documents and multimedia can be read or watched/listened to.

Web crawler – internet bot that systematically browses the

world wide web to update its web page content.

White-box testing – a method of testing a program that tests the

structure and logic of every path through a program module.

Wi-Fi – wireless connectivity that uses radio waves, microwaves.

WIMP – windows, icons, menu and pointing device.

Winding – process which occurs when a recursive function or

procedure is called until the base case is found.

WLAN – wireless LAN.

WNIC – wireless network interface cards/controllers.

Word – group of bits used by a computer to represent a single unit.

World Wide Web (WWW) – collection of multimedia web pages

stored on a website; uses the internet to access information

from servers and other computers.

WPAN – wireless personal area network; a local wireless network

which connects together devices in very close proximity

(such as in a user’s house); typical devices would be a laptop,

smartphone, tablet and printer.

Write – file access mode in which data can be written to a file;

any existing data stored in the file will be overwritten.

Zero compression – way of reducing the length of an IPv6

address by replacing groups of zeroes by a double colon (::);

this can only be applied once to an address to avoid

ambiguity.