OCR GCSE Computer Science Glossary

1D

A 1D array contains a one-dimensional sequence of elements. A single index number identifies each element.

2D

A 2D array organises data in a table-like structure. Each data item is identified by two numbers – the row number, then the column number.

Abstraction

Abstraction simplifies a problem by including only the necessary facts to solve it.

Accumulator (ACC)

The accumulator stores the results of each calculation the arithmetic/logic unit (ALU) performs.

Algorithm

An algorithm defines the logical or mathematical steps to solve a problem. It must be accurate, repeatable, and understandable.

AND

The Boolean operator AND joins two Boolean expressions to create a new one. If both parts of the expression are True, then the new expression is True. If either part of the expression is False, then the new expression is False.

Array

An array exemplifies a data structure. It has an identifier and stores many data values.

Arithmetic/logic unit (ALU)

The arithmetic/logic unit (ALU) processes data using binary maths and logic.

Arithmetic operator

Arithmetic operators carry out numerical operations and change number values.

ASCII

ASCII serves as a common character set in coding. It contains fewer than 255 codes and includes only basic keyboard characters.

Assign

Assigning gives a value to a variable using the equals sign.

Authentication

Authentication checks user identity to stop the wrong people from using a programme.

Bandwidth

Bandwidth measures the number of signals that can travel through the transmission media of the network connection simultaneously.

Binary

Binary is base 2, meaning that binary numbers are made out of two digits: 1 and 0.

Binary search

A binary search finds a value in an array by identifying the middle value and comparing it to the search term. It splits the array in half, removing the lower half if the term is larger than the middle value, or the upper half if it is smaller. This process repeats until the array is reduced to one element.

Binary Shift

A binary shift moves all the bits in a binary number to the left or right to multiply or divide.

Biometrics

Biometrics authenticate a user by using physical characteristics, such as a thumbprint. (See ‘authentication’.)

Bit

A bit, short for ‘binary digit,’ is a single digit in a binary number and can have the value 1 or 0.

Bit depth

Bit depth measures the number of bits in an audio sample. A greater bit depth produces more realistic and natural sound.

Bluetooth

Bluetooth enables digital communication with nearby devices.

Boolean / Boolean expression

Boolean, or Boolean expressions, represent a data type that is either True or False.

Boolean operator

Boolean operators combine Boolean expressions to create a larger Boolean expression.

Boundary data

Boundary data, a type of test data, shows inputs that are on the edge of being incorrect.

Bubble sort

A bubble sort is an algorithm that works by traversing the array with a for loop, swapping values that are the wrong way round. It repeats this traversal until no more swaps are needed.

Byte

A byte consists of eight bits, each with a different place value.

Cache

A cache is a small area of fast-access memory. Use of cache speeds up computer processes.

Called

A procedure is called by including the name of the procedure in the main program. The commands inside the procedure will be carried out when the procedure is called.

Carry bit

A carry bit is an additional number in binary arithmetic that is ’carried’ to the next column if the result is larger than 1.

Case / switch

The switch structure is a form of conditional structure that gives a range of possible values for a variable. Each possible value is called a case. Each case is followed by a different set of commands.

Casting

Casting is when the data type of a variable is changed. It is also called type-casting.

Central processing unit (CPU)

The central processing unit (CPU) is the processor that controls and executes operations. It includes the control unit (CU) and arithmetic/logic unit (ALU).

Character

A character is a data type that holds a single text character.

Client-server

A client-server a type of computer network. The server holds most of the files and the clients get their files from the server.

Clock signals

Clock signals are regular pulses of electricity that are sent out by the control unit (CU) to time the fetch-execute cycles.

Clock speed

Clock speed is the speed by which clock signals are sent out. The faster the speed, the faster the computer will run.

Closed file

When you close a file, the system removes it from active memory, preventing further edits.

Colour depth

Colour depth defines how many bits a system uses to store each pixel’s colour code. Increasing the colour depth allows the system to display more realistic colours.

Comment

Programmers write comments in their code to help human readers understand what the code does. The computer ignores these comments during execution. In exam reference language, comments start with the // symbol.

Comparison operator

Programmers use comparison operators to compare two values. These operators, also known as relational operators, include symbols like > and ==.

Compiler

A compiler translates an entire program by reading it, converting it into machine code, and saving the result as a new file.

Concatenation

Concatenation joins strings together to create a new, longer string.

Condition-controlled loop

A condition-controlled loop uses a Boolean expression to determine whether it should continue running. Programmers use keywords like while or until to define these loops, especially when they don’t know in advance how many times the loop should repeat.

Constant

A constant stores a value that stays the same while the programme runs.

Control unit (CU)

The control unit (CU) manages all other parts of the computer. It sends signals that direct each component on what actions to perform.

Copyright

Copyright gives creators the legal rights to their work. It lets them control who can copy or use it, ensures they’re credited as the creator, and allows them to earn money from its use.

Count-controlled loop

A count-controlled loop repeats a specific number of times. Programmers use the keyword for to create this type of loop when they know in advance how many repetitions are needed.

Cultural

Cultural ideas and creations include things such as art, media and crafts which enrich our society.

Database

A database organises data into structured tables for easy access and management.

Data protection

Data protection is the protection of personal data. It is upheld by the Data Protection Act, which was extended in 2018 as the GDPR (General Data Protection Regulations).

Data type

Every program assigns a data type to each value or expression, based on how it stores the data. Programmers commonly use data types like integer, float, string, and Boolean

Decomposition

Programmers use decomposition to break a large problem into smaller, manageable parts. Solving, writing, and testing these smaller problems becomes much easier.

Default

When none of the cases in an algorithm match, the program runs the commands under the default case.

Denary

People use the denary number system in everyday life. It operates on base 10, meaning that numbers in denary are made out of ten digits (0 to 9).

Denial of service

Denial of service (DoS or DDoS) occurs when authorised access to a network is interrupted. Hackers do this by overloading the network with requests.

Device driver

A device driver enables your computer to control peripheral devices by providing the necessary software interface.

Diagnostic / error diagnostic

A diagnostic tool identifies errors in your code and explains what’s wrong.

Digital data

Digital systems use on/off signals to represent data, encoding them as binary numbers.

Digital technology

Digital technology refers to devices that process data in digital form.

Domain name

A domain name uses text to identify web resources like web pages.

Ethernet connects computers to a network using a standard cable-based method.Elements

An array stores data values called elements. Each element uses the array’s name followed by an index number to identify it.

Else

Programmers use the keyword ‘else’ in conditional structures. The structure starts with ‘if’ and a logical test. If the test fails, the program runs the commands that follow ‘else’.

Elseif

Elseif commands are used to build conditional structures with multiple logical tests. Each ‘elseif’ is followed by a different logical test.

Embedded system

Devices like cars and fridges use embedded systems that include built-in processors to control specific functions.

Encryption

Encryption scrambles digital signals using a hidden code, allowing only those with the encryption key to read the message.

Erroneous data

Testers use erroneous data to check how a program responds to user mistakes.

Error message

An error message points out a problem in the program, showing what type of error occurred and where it happened.

Ethernet

Ethernet connects computers to a network using a standard cable-based method.

Ethics

Ethics defines the rules that guide people to distinguish right from wrong.

Environment

The environment includes the natural world—the biological and physical surroundings we live in.

Fetch-execute cycle

The fetch-execute cycle moves data and instructions through the processor while the computer runs. This process, also known as the instruction cycle.

Field

A field stores a single item of data in a data table. Each record in the table includes the same set of fields, which appear as columns.

Final testing

Testers perform final testing after programmers finish developing the code and prepare the program for release or sale. This stage checks the entire program to ensure it works as intended.

Firewall

A firewall is a piece of hardware which uses built-in software to inspect every signal entering or leaving a network, protecting it from unauthorised access.

Fixed length

A fixed-length data structure, such as an array, maintains a constant size that doesn’t change during execution

Flash storage

Flash storage stores data using solid-state technology and appears in devices like USB sticks, solid-state drives (SSDs), and SD cards. It’s also known as solid-state storage.

Float

The float data type, also known as real, stores numbers that include decimal points.

Flowchart

Flowcharts use diagrams made of boxes and arrows to map out the structure of an algorithm, showing the sequence of actions step by step.

For loop

A ‘for loop’ controls repetition by using a counter variable and starting with the keyword ‘for’. The loop repeats a set number of times, based on the value stored in the counter. The variable stores the number of repeats.

Function

Functions carry out commands and return a new value to the main programme.

General Data Protection Regulation (GDPR)

The General Data Protection Regulation (GDPR) is a Europe-wide agreement which upholds the UK Data Protection Act.

Global variable

A global variable allows any part of the program—including all procedures and functions—to access and use its value.

Hackers

Hackers attempt to disrupt computer networks or gain unauthorised access to them.

Hexadecimal

Hexadecimal uses base 16, so it represents numbers using 16 distinct digits.

High level language

Programmers use high-level languages like Python, Java, and C++ because these languages align with how humans think and work. Most programs are written in high-level languages.

If

A conditional structure begins with the keyword if and a logical test. The commands that follow are carried out if the test is true.

Indented

Programmers indent commands by setting them in from the edge of the page or screen to show the structure of a program. They indent commands inside structures like loops to make the code easier to read and understand.

Index number

An index number identifies an element’s position in an array and appears in square brackets [ ].

Input

An IPO model begins with inputs—starting facts or values—that the program processes to produce outputs.

Insertion sort

An insertion sort is an algorithm that works by traversing the array, and passing any items that are out of place backwards to their correct position. It is typically slightly faster than the bubble sort.

Integer

Programmers use the integer data type to represent whole numbers without decimal points.

Integrated development environment (IDE)

Programmers use an integrated development environment (IDE)—software designed specifically for writing code—to develop their programs efficiently.

Intellectual property rights (IPR)

Intellectual property rights (IPR) protect creations of the mind—such as inventions, computer programs, and designs—by granting legal rights to their creators.

Interpreter

An interpreter translates code by reading one command at a time and immediately instructing the computer to execute it, without creating a new file.

Invalid data

Invalid data is a type of test data. Testers use invalid data to check how a programme handles inputs it doesn’t allow. This type of test data helps identify errors in input validation.

IP address

An IP address is provided to every device with an internet connection. IP stands for ‘internet protocol’. Devices use this address to send signals to the correct destination online.

IPO (input, processing, output) model

The IPO model (Input, Processing, Output) outlines how a programme or algorithm works. It takes inputs, processes them, and produces outputs.

Iteration

Iteration involves repeating actions. Programmers use loops as iterative structures to execute code multiple times.

Iterative testing

Developers perform iterative testing throughout a program’s development. They repeatedly test the program until they find and fix all errors.

Least significant bit

A byte stores bits in different positions, and the ‘least significant bit’ sits in the spot with the smallest place value. This bit affects the number the least, but it’s still important.

License

A license allows a person or group of people to use software, usually for a fee.

Linear search

A linear search uses a for loop to go through an array and compare each item to the search term. When it finds a match, it identifies the item as found.

Local area network (LAN)

A local area network (LAN) joins computers that are close to each other, such as those on the same building or site.

Local variable

A subroutine creates a local variable and allows it to be used only within that subroutine.

Logic circuit

A logic circuit is formed by joining logic gates together.

Logic diagram

A logic diagram shows how logic gates are wired together to form a logic circuit.

Logic gate

A logic gate takes inputs and converts them into outputs using a special circuit.

Logical error

A program produces a logical error when it gives unwanted or unexpected output.

Loop structure

A loop structure repeats one or more commands, a process also known as iteration.

Lossless compression

Lossless compression reduces a file’s size without removing any data, so it keeps the original quality, even though the file may not shrink as much as with lossy compression.

Lossy compression

Lossy compression reduces a file’s size by removing some data, which causes a loss in quality.

Low level language

Programmers use Low level language, such as machine code and assembly language, to write instructions that closely match the way computers work. This includes machine code and assembly language. These languages are less easy to use than high level languages.

MAC address

Manufacturers assign a MAC address to each digital device to identify it. This ‘media access control’ address directs signals on a local network to the correct device.

Magnetic storage

Magnetic storage is a form of storage that is magnetic, such the hard drive of a computer or magnetic tape.

Maintainable

A maintainable program is easy to correct, improve, and extend.

Malware

Malware refers to malicious software such computer viruses that can force your computer to perform unwanted actions.

Memory / memory unit

A computer uses memory to store the data and instructions it needs while operating, holding them in live electrical circuits.

Memory address register (MAR)

The memory address register (MAR) holds the memory address to fetch from during the fetch part of the fetch-execute cycle, and the address to save to during the store part of the cycle.

Memory data register (MDR)

The memory data register (MDR) stores data fetched from memory during the fetch part of the cycle, and holds data ready to be written back during the store part of the cycle.

Merge sort

A merge sort algorithm splits the array into single items, then repeatedly merges them into increasingly larger sorted arrays until it forms a single fully sorted array.

Mesh topology

A mesh topology connects devices through multiple pathways, ensuring the network remains stable and operational even if some connections fail.

Metadata

The additional image information held in some image files. It stores information such as the size or shape of the image.

Method

Programmers use methods as a type of subroutine, similar to functions but written slightly differently.

Modular testing

Modular testing focuses on testing individual modules of a program, making the process quicker and easier than testing the entire programme.

Modulus

A modulus is an arithmetic operator which divides one number by another and shows the remainder only.

Most significant bit

The bit with the largest place value in a byte determines the most significant bit.

Multi-tasking

A single computer runs more than one application at the same time when it performs multi-tasking.

Network

Computers form a network by connecting through digital communication links.

Network interface controller (NIC)

A network interface controller (NIC) uses electronic components to let a computer send and receive network signals.

Nibble

A nibble groups four bits together.

Normal data

Normal data is a type of test data. It tests the effect of normal, expected inputs.

NOT

NOT is a Boolean operator that reverses the value of a Boolean expression.

Open file

The system copies an open file into memory so it can be read or edited.

Open-source

Open-source software is usually free to use and copy without charge.

Operating system

An operating system bundles together all the systems software needed to make the computer work properly. It is usually installed when you buy a computer.

Optical storage

A laser beam reads data from optical storage devices such as CDs, DVDs, or BluRay discs.

OR

The OR Boolean operator joins two Boolean expressions to create a new one. If either expression is True, the operator makes the whole expression True. If both expressions are False, the operator makes the new expression False.

Output

The outputs are the answers or values you need from a program. The outputs are made by transforming the inputs to the programme.

Parameter

A parameter is used like a variable inside a subroutine. The value of the parameter is sent from the main programme when the subroutine is called.

Password

A person proves their identity with a password when they log on to a network.

Peer-to-peer

In a peer-to-peer network, all computers share an equal relationship, sending and receiving files without any one computer taking priority.

Peripherals

Peripherals are input and output devices that are connected to the processor.

Pharming

Pharming is when someone tries to trick people by creating a fake website.

Phishing

Phishers try to trick people by sending fake emails.

Pixel

Pixels, short for ‘picture elements,’ form digital images by combining tiny dots or points of light.

Predefined function

A predefined function is a ready-made function included in most programming languages.

Pre-requisite

Every process depends on certain conditions, called prerequisites, to function correctly. For example, the binary search algorithm needs a sorted array before it can run.

Primary storage

Computers access data more quickly from primary storage—also called RAM or memory—than from secondary storage.

Privacy

People protect their privacy by keeping certain personal information hidden from public view. Technology users should handle others’ information with care and respect their privacy.

Procedure

A procedure is a type of subroutine that carries out commands when called by the main programme. Each procedure uses a unique name or identifier.

Processing

In an IPO model, a process transforms inputs into outputs through a series of steps. In a computational problem, these steps must follow logical or mathematical rules.

Programme counter (PC)

The programme counter (PC) holds the address for the next instruction and steps through the programme line by line during the fetch-execute cycle.

Proprietary

Proprietary software is owned by the people or organisation that made it. They earn money by selling licenses to use the software.

Protocol

A protocol is a standard for communication, such as hypertext transfer protocol (HTTP).

Pseudocode

Pseudocode is pretend program code. Programmers often write algorithms in pseudocode—a simplified, language-neutral way of writing code—so others can easily understand it, regardless of the programming language they use.

Quotient

A quotient is an arithmetic operation which divides one number by another and shows the whole number part of the result.

RAM

RAM stands for Random Access Memory (RAM). It is also known as memory.

Readable

Programmers find it easier to understand a readable program, which improves its maintainability.

Read from

Read from is a file operation which gives you a value from a file in storage.

Read-only access

With read-only access, users can view files but not make changes.

Read-write access

With read-write access, users can view and make changes to files.

Real

The real data type, also known as float, stores numbers that include a decimal point.

Record

A record stores all the information about an item in a single row of a data table.

Registers (PC, MDR, MAR, ACC)

Registers are the tiny memory locations in the processor that hold a single binary number – typically either data or the address of a memory location.

Relevant

Relevant facts are the pieces of information that solve a problem.

Resolution

Resolution is the number of pixels used to form an image. The higher the resolution, the greater the number of pixels, and the higher the quality of the image.

Returned value

A returned value is the value returned to the main program by a function.

ROM

ROM, or Read-Only Memory, stores the start-up instructions for a computer. The contents of ROM cannot change.

Router

A router connects one network to another.

Run-time environment

The run-time environment lets the user input values, and shows the outputs and any run-time errors of the programme.

Run-time error

A run-time error occurs when a programme tries to make the computer perform an impossible task. This action can cause the programme to crash.

Sample rate

The sample rate measures how many times per second the system samples a sound. Increasing the sample rate improves the sound quality.

Search algorithms

Search algorithms use different methods to find a value in a data structure.

Search condition

A search condition defines the criteria used to search a data table, such as in the SQL language.

Search term

The search term is the value being searched for in a search algorithm.

Secondary storage / storage

Secondary storage is used to hold instructions and data that are not in use. They are held as files in storage. It does not rely on electricity. Secondary storage is also called storage.

SELECT… FROM… WHERE

SELECT… FROM… WHERE are structured query language (SQL) keywords. SELECT lets you choose specific fields, FROM specifies the data table to search, and WHERE filters the results to find individual records.

Selection

A selection structure directs an algorithm to choose between different actions based on a condition—often using an if statement (see ‘If’ section).

Sequence

A sequence is a linear series of commands which are carried out one at a time in the order they are given in the algorithm.

Sequential algorithm

A sequential algorithm follows a specific order of commands, executing each one step by step.

Slicing

Slicing a string means to make a substring by copying part of the original string.

Social engineering

Social engineering occurs when someone tries to trick people into sharing their password or personal information such as banking details.

Solid state storage

Solid state storage, also known as flash memory, stores data by trapping electrons in solid material.

Sort algorithm

A sort algorithm arranges the elements of an array in a specific order, using one of several available methods.

Sorted array

A sorted array arranges its values in numerical or alphabetical order.

SQL

Structured Query Language (SQL) is a specialist language to work with databases.

SQL injection

SQL injection is a form of hacking. It is used to edit or delete data in a database without permission. 

Star topology

A star topology is a type of network. It is easy to set up and works by connecting all computers to a central hub or switch

String

A string is a data type that stores text characters, usually shown in quote marks.

Structured code

Developers create structured code by breaking it down into smaller subsections through decomposition.

Structure diagram

A structure diagram shows the sub programmes that make up a programme.

Sub program / subroutine

A sub program is a block of code from a larger programme that is saved using an identifier.

Substring

A substring is a new string that is made by copying part of an original string.

Switch

A switch connects several computers in a network. It checks each message and sends it to the right computer.

Syntax

Syntax defines the rules that programmers follow when writing a programme.

Syntax error

The code triggers a syntax error when it breaks the rules of the programming language.

Table

A table stores data by organising all the facts about a particular topic or subject.

Test data

Test data is the inputs used when testing a programme. A wide range of test data should be used.

Trace an algorithm

Tracing an algorithm means going through the algorithm on paper, recording how the variable values change.

Trace table

A trace table is used to trace an algorithm. It includes a column for each variable, one for the line number, and one for the outputs.

Translator

A translator converts commands into signals the computer understands.

Transmission media

Transmission media carries signals between computers in a network.

Truth table

A truth table displays the inputs and outputs of a logic circuit or gate.

Unicode

Unicode provides a common character set with thousands of codes, including global alphabets, symbols, and emojis. It supports more characters than ASCII but uses more memory space.

Until loop

An ‘until loop’ controls repetition using a condition and the keyword until. It places the logical test at the end of the loop.

User access levels

User access levels control how people interact with files. A person might have no access to some files, read-only access to others, or full access to read and modify certain files.

User-friendly

A user-friendly programme guides users with clear messages and prompts, making it easy for them to enter the correct values.

User interface

The user interface is how you control and interact with the computer.

Utilities

Utilities are types of system software that carry out useful tasks.

Validation

Validation means checking inputs before they are used in a program, and stopping any bad inputs.

Variable

A variable stores values in a named memory location.

Virtual memory

Virtual memory means using storage as memory. For example, if memory is too full. It is not accessed as quickly as memory.

Volatile

Volatile memory stores data using electricity. When the computer loses power, it erases the memory’s contents. RAM functions as volatile memory, while ROM does not.

Von Neumann architecture

Von Neumann architecture defines the structure of most modern computers. It includes the processor, which performs all the computer’s tasks, along with input and output devices.

Web hosting

Web hosting is when a server hosts a web page so people can view it over the internet.

Web server

A web server is a computer which connects to the internet full-time to serve web content.

While loop

A while loop is a condition-controlled loop which uses the keyword while. The commands between while and endwhile will be repeated.

Wide area network (WAN)

A wide area network (WAN) connects computers across different sites, cities, or countries.

Wi-Fi

Wi-Fi enables devices to send and receive wireless signals.

Wireless access point (WAP)

A wireless access point (WAP) sends out signals such as radio waves, to make a wireless connection.

Write to

‘Write to’ is a file operation that involves copying a value into a file and saving it in storage.