OCR GCSE Computer Science Glossary
The key vocabulary you need to learn for your OCR GCSE Computer Science paper. Find all the terms and definitions you need to understand, from ‘1D’ to ‘write to‘.
1 - A (1D to authentication)
A 1D array is a one-dimensional sequence of elements. Each element is identified by a single index number.
A 2D array is a two-dimensional table-like data structure. Each data item is identified by two numbers – the row number, then the column number.
Abstraction means simplifying a problem to include only the facts that are necessary to solve it.
The accumulator saves the results of each calculation carried out by the arithmetic/logic unit (ALU).
An algorithm sets out the logical or mathematical steps to solve a problem. It should be accurate, repeatable, and understandable.
AND is a Boolean operator that joins two Boolean expressions to make a new Boolean expression. 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.
An array is an example of a data structure. It has an identifier and can store many data values.
arithmetic/logic unit (ALU)
The arithmetic/logic unit (ALU) is the component that processes data using binary maths and logic.
Arithmetic operators carry out numerical operations and change number values.
ASCII is a common character set used in coding. It has fewer than 255 codes and includes only basic keyboard characters.
To assign is to give a value to a variable using the equals sign.
Authentication is any method of checking user identity to stop the wrong people from using a program.
B (Bandwidth to byte)
Bandwidth is the number of signals that can travel through the transmission media of the network connection at one time.
Binary is base 2, meaning that binary numbers are made out of two digits: 1 and 0.
A binary search is a way of finding a value in an array. It identifies the middle value and compares it to the search term. It splits the array in half. If the term is bigger than the middle value, it removes the lower half. If it is smaller, it removes the upper half. This process is repeated until the array is reduced to one element.
A binary shift means moving all the bits in a binary number to the left or right in order to multiply or divide.
Biometrics are the use of physical characteristics, such as a thumbprint, to authenticate a user. (See ‘authentication’.)
A bit is a single digit in a binary number. The term is short for ‘binary digit’. A bit can have the value 1 or 0.
Bit depth is the number of bits of information in an audio sample. The greater the bit depth, the more realistic and natural the sound.
Bluetooth is a standard for digital communication with devices that are nearby.
Boolean / Boolean expression
Boolean, or Boolean expressions, is a data type which is either True or False.
Boolean operators are used with Boolean expressions to make a larger Boolean expression.
Boundary data is a type of test data. It shows inputs which are on the edge of being incorrect.
A bubble sort is an algorithm that works by traversing the array with a for loop, swapping values that are the wrong way round. The traversal is repeated until there are no more swaps to be made.
A byte is a group of eight bits, each with a different place value.
C (Cache to clock speed)
A cache is a small area of fast-access memory. Use of cache speeds up computer processes.
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.
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 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).
A character is a data type that holds a single text character.
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 are regular pulses of electricity that are sent out by the control unit (CU) to time the fetch-execute cycles.
Clock speed is the speed by which clock signals are sent out. The faster the speed, the faster the computer will run.
C (Closed file to cultural)
When a file is closed it is removed from active memory and cannot be edited.
Colour depth is the number of bits used to store the colour code for each pixel in an image. The greater the colour depth, the more realistic the colour.
A comment is text in a program that is ignored by the computer. Comments are there to help the human reader and explain the code. In exam reference language, comments begin with a // symbol.
Comparison operators are used to compare two values. They may also be called relational operators. Examples include > and ==.
A compiler is a type of translator which works by reading the whole program, turning it into machine code, and saving it as a new file.
Concatenation means joining strings together to make a new, longer string.
A condition-controlled loop is controlled by a Boolean expression. The keywords while or until indicate a condition-controlled loop. This type of loop may be used when the programmer doesn’t know in advance how many repeats are needed.
A constant is a stored value that will not change while a program is running.
control unit (CU)
The control unit (CU) is the component that controls all the other parts of the computer. It sends signals telling the other parts what to do.
Copyright is the rights to a piece of work someone has made. It includes the right to decide who can copy or use the work, the right to be identified as creator, and the right to get paid for use of the content.
A count-controlled loop repeats a set number of times. The keyword for indicates a counter-controlled loop. This type of loop may be used if the programmer knows in advance how many times to repeat the loop.
Cultural ideas and creations include things such as art, media and crafts which enrich our society.
D (Database to domain name)
A database is a collection of structured data tables.
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).
Every value or expression in a program has a data type. The data type is related to how the value is stored. The main data types are integer, float, string, and Boolean.
Decomposition is when programmers break a big problem down into smaller parts. Smaller problems are easier to solve, easier to write, and easier to test.
Default occurs if none of the cases in an algorithm match. The commands that follow default are then carried out.
Denary is the number system that people use in their daily lives. It is base 10, meaning that numbers in denary are made out of ten digits (0 to 9).
denial of service
Denial of service occurs when authorised access to a network is interrupted. Hackers do this by overloading the network with requests. It is also called DoS or DDoS.
A device driver is the software that lets your computer control peripheral devices.
diagnostic / error diagnostic
A diagnostic is a way to identify errors in code and tell you what is wrong.
Digital data is made of on/off signals that can be represented using binary numbers.
Digital technology is the term used for any device that processes data in digital form.
A domain name uses text to identify every web resource, such as a web page.
E (Elements to environment)
Elements are the data values of an array. Each element is given the name of the array, plus an index number.
Else is a programming keyword used in conditional structures. The structure begins with the keyword if and a logical test. The commands following ‘else’ are carried out if the test is false.
An elseif command is used to create a conditional structure with multiple logical tests. Each elseif is followed by a different logical test.
An embedded system is a device such as a car or fridge that contains an embedded processor.
Encryption scrambles digital signals using a hidden code, meaning that only people with the encryption key can read the message.
Erroneous data is a type of test data. It is used to test the effect of user errors on the program.
An error message identifies an error in a program, showing what type of error has been found and where it is in the program.
Ethernet is a standard for connecting computers to a network using a cable.
Ethics means the rules of right and wrong.
The environment means the natural world: the biological and physical world in which we live.
F (Fetch-execute cycle to function)
The fetch-execute cycle is the process by which data and instructions are passed round the processor when the computer is working. It is also sometimes called the instruction cycle.
A field is one item of data stored in a data table. All the records in the data table include the same fields. The fields are shown as columns of the table.
Final testing is carried out when the programmers have finished developing the code and the program is ready to be used or sold. It tests the whole program.
A firewall is a piece of hardware with its own software. It reads and checks every signal that goes in or out of a network.
A fixed length data structure, such as an array, is a data structure that does not change in size.
Flash storage is a form of storage such as a USB stick, solid-state drive or SD card. It is also known as solid-state storage.
Float (also known as real) is a data type. It stores numbers that include a decimal point.
Flowcharts are diagrams that show the structure of an algorithm. They are made of boxes joined by arrows which show the sequence of actions.
A for loop is a count-controlled loop which starts with the keyword for. It includes a variable called a counter. The variable stores the number of repeats.
Functions carry out commands and return a new value to the main program.
G - I (General Data Protection Regulation (GDPR) to iterative testing)
The General Data Protection Regulation (GDPR) is a Europe-wide agreement which upholds the UK Data Protection Act.
A global variable is a variable that can be used anywhere in the program, in any procedure or function.
Hackers are people who try to stop a computer network from working, or who try to gain unauthorised access to a network.
Hexadecimal is base 16, meaning that hexadecimal numbers are made of 16 digits.
high level language
A high level language is a type of programming language that suits the way humans work. Examples include Python, Java, and C++. Most programs are written in high level languages.
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 commands are set in from the edge of the page or screen. Indentation is used to show the structure of a program. Commands inside a structure such as a loop are indented.
An index number shows the position of an element in an array. The index number is given in square brackets [ ].
The inputs are the starting facts or values of an IPO model. They are input to the program and processed to create outputs.
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.
An integer is a data type. Integers are whole numbers with no decimal point.
integrated development environment (IDE)
An integrated development environment (IDE) is software designed especially for writing programs. Most programmers use an IDE when they write programs.
intellectual property rights (IPR)
Intellectual property rights (IPR) protect things that people create, such as inventions, computer programs, and designs.
An interpreter is a type of translator which works by reading one command at a time and making the computer carry out that command. It does not create a new file.
Invalid data is a type of test data. It is used to test inputs which are not allowed by the program.
An IP address is provided to every device with an internet connection. IP stands for ‘internet protocol’. The IP address is used to send signals on the internet to the right destination.
IPO (input, processing, output) model
The IPO (input, processing, output) model describes the structure of a program or algorithm. Inputs are processed to create outputs.
Iteration means repetition. A loop is an iterative structure.
Iterative testing means testing a program during development. Testing is repeated many times during the development of a program until no more errors are found.
L (Least significant bit to low level language)
least significant bit
The least significant bit is the bit with the smallest place value in a byte.
A license allows a person or group of people to use software, usually for a fee.
A linear search uses a for loop to traverse an array, comparing each item to the search term. If it matches, the item is 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.
A local variable is a variable that is created inside a subroutine, and can only be used inside that subroutine.
A logic circuit is formed from logic gates that have been joined together.
A logic diagram is a drawing that shows how logic gates have been wired together to make a logic circuit.
A logic gate is a special circuit that changes inputs into outputs.
A logical error is when a program produces unwanted or unexpected output.
A loop structure includes one or more commands which are repeated. It is also called iteration.
Lossless compression is a way of compressing file size without losing quality, but the file may not get as small as when lossy compression is used.
Lossy compression is a way of compressing file size, but with some loss of quality.
low level language
Low level language is a programming language which matches the way computers work. This includes machine code and assembly language. These languages are less easy to use than high level languages.
M (MAC address to multi-tasking)
A MAC address is added by the factory to identify every digital device. MAC stands for ‘media access control’. This address directs signals on a local network to the correct device.
Magnetic storage is a form of storage that is magnetic, such the hard drive of a computer or magnetic tape.
A maintainable program is easy to correct, improve, and extend.
Malware refers to malicious software such as a computer virus, which might make your computer do something you don’t want it to.
memory / memory unit
The part of a computer which holds the data and instructions that the computer needs while it is working. They are held using 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) holds data that has been fetched from memory during the fetch part of the cycle, and holds data ready to be saved in the store part of the cycle.
A merge sort is an algorithm that works by splitting the array into single items, merging them to make larger and larger arrays in sorted order. Eventually, all the items are in a single sorted array.
A mesh topology is a type of network with many connections between the different devices. It is stable and continues to operate even if some connections break.
The additional image information held in some image files. It stores information such as the size or shape of the image.
A method is a type of subroutine. Methods are similar to functions, but are written slightly differently.
Modular testing means testing the modules of a program. It is quicker and easier than testing the whole program.
A modulus is an arithmetic operator which divides one number by another and shows the remainder only.
most significant bit
The most significant bit is the bit with the largest place value in a byte.
Multi-tasking means that more than one application is running at the same time on a single computer.
N - P (Network to peripherals)
A network is a set of computers that are connected by digital communication links.
network interface controller (NIC)
A network interface controller (NIC) holds the electric components that let a computer send and receive network signals.
A nibble is a group of four bits.
Normal data is a type of test data. It tests the effect of normal, expected inputs.
NOT is a Boolean operator that reverses the value of a Boolean expression.
An open file is a file copied into memory so it can be read or edited.
Open-source software is usually free to use and copy without charge.
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 is a form of storage such as a CD, DVD or BluRay. The storage is read by a laser beam.
OR is a Boolean operator that joins two Boolean expressions to make a new Boolean expression. If either part of the expression is True, then the whole expression is True. If both parts of the expression are False, then the new expression is False.
The outputs are the answers or values you need from a program. The outputs are made by transforming the inputs to the program.
A parameter is used like a variable inside a subroutine. The value of the parameter is sent from the main program when the subroutine is called.
A password helps to prove a person’s identify when they log on to a network.
A peer-to-peer network has equal relationship between computers. All computers can send and receive files with no computer being more important.
Peripherals are input and output devices that are connected to the processor.
P (Pharming to pseudocode)
Pharming is when someone tries to trick people by using a pretend website.
Phishing is when someone tries to trick people by using a pretend email.
A pixel is short for ‘picture element’. Pixels are dots or points of light that combine to form a digital image.
A predefined function is a ready-made function included in most programming languages.
A pre-requisite is a requirement that must be in place for a process to work. For example, it is a pre-requisite of the binary search algorithm that the array is sorted.
Primary storage is another name for computer memory or RAM. It is faster to access than secondary storage.
Privacy means that some information about an individual is protected from public view. Technology users should be careful to respect other people’s privacy.
A procedure is a type of subroutine that carries out commands when called by the main program. Each procedure has a name or identifier.
Processing means the steps that transform inputs to outputs in an IPO model. In a computational problem these steps must be steps of logic or maths.
program counter (PC)
The program counter (PC) holds the address for the next instruction to be executed. It counts through a program line by line during the fetch-execute cycle.
Proprietary software is owned by the people or organisation that made it. They earn money by selling licenses to use the software.
A protocol is a standard for communication, such as hypertext transfer protocol (HTTP).
Pseudocode is pretend program code. Programmers often write algorithms in pseudocode as it is a way of writing code which other programmers can understand, no matter which programming language they use.
Q - R (Quotient to run-time error)
A quotient is an arithmetic operation which divides one number by another and shows the whole number part of the result.
RAM stands for Random Access Memory (RAM). It is also known as memory.
A readable program is easier for other programmers to understand. Readability makes a program easier to maintain.
Read from is a file operation in which you get a value from a file in storage.
Read-only access allows someone to view files but not to make changes.
Read-write access allows someone to view and make changes to files.
Real (also known as float) is a data type used to store numbers that include a decimal point.
A record is all the information about an item, stored as one 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 facts are the pieces of information needed to solve a problem.
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.
A returned value is the value returned to the main program by a function.
ROM stands for Read-Only Memory. The contents of ROM cannot change. It is used to store the start-up instructions for a computer.
A router connects one network to another.
The run-time environment lets the user input values, and shows the outputs and any run-time errors of the program.
A run-time error is an error in a program that happens when the program tries to make the computer do something impossible. This can make the program crash.
S (Sample rate to sort algorithm)
Sample rate indicates how many times per second a sound is sampled. The higher the sample rate, the better the sound quality.
Search algorithms are different ways of searching for a value in a data structure.
A search condition specifies the conditions for a data table search, for example in the SQL language.
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 allows you to select data from certain fields. FROM allows you to specify the name of the data table to be searched. WHERE allows you to pick out individual records from the data table.
A selection structure is an algorithm which includes a choice between different actions. (See ‘if’.)
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.
A sequential algorithm is an algorithm with a sequence of commands.
Slicing a string means to make a substring by copying part of the original string.
Social engineering is when someone tries to trick people into sharing their password or personal information such as banking details.
solid state storage
Solid state storage is another word for flash memory. It holds data using electrons trapped in solid matter.
A sort algorithm is a method for sorting an array. There are several different methods.
S (Sorted array to syntax error)
A sorted array means the values in the array are in numerical or alphabetical order.
SQL means Structured Query Language. It is a specialist language used to work with databases.
SQL injection can be used to edit or delete data in a database without permission. It is a form of hacking.
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
A string is a data type that can hold text characters. The text is usually shown in quote marks.
Structured code is code that has been broken down into subsections (decomposition).
A structure diagram is used to show the sub programs that make up a program.
sub program / subroutine
A sub program is a block of code from a larger program that is saved using an identifier.
A substring is a new string that is made by copying part of an original string.
A switch connects several computers in a network. It checks each message and sends it to the right computer.
Syntax means the rules of a program which you follow when writing the program.
A syntax error occurs when the code breaks the rules of the language the program is written in.
T - U (Table to utilities)
A table is a way of storing data, including all the facts about a particular topic or subject.
Test data is the inputs you will use when testing a program. A wide range of test data should be used.
trace an algorithm
Tracing an algorithm means going through the algorithm on paper, recording the changing values of the variables.
A trace table is used to trace an algorithm. it should include a column for each variable in the algorithm, a column for line number and a column for outputs.
A translator turns commands into signals the computer can understand.
Transmission media carries signals between computers in a network.
A truth table is a table that summarises the inputs and outputs of a logic circuit or gate.
Unicode is a common character set. It has thousands of codes, including all global alphabets, symbols, emojis, etc. It has more characters than ASCII, but uses more space in memory.
An until loop is a condition-controlled loop which uses the keyword until. In an until loop the logical test is at the end of the loop.
user access levels
User access levels allow people different levels of access to different files. A person may have no access to some files, be able to only read some files, or be able to read and change other files.
A user-friendly program is easy to use. It has clear messages and prompts that help the user to input the right values.
The user interface is how you control and interact with the computer.
Utilities are types of system software that carry out useful tasks.
V - W (Validation to write to)
Validation means checking inputs before they are used in a program, and stopping any bad inputs.
A variable is a named memory location where values are stored.
Virtual memory means using storage as memory. For example, if memory is too full. It is not accessed as quickly as memory.
Volatile memory uses electricity to hold data. The contents of memory are lost if the computer’s power is turned off. RAM is volatile memory. ROM is not volatile.
von Neumann architecture
von Neumann architecture defines the structure of most modern computers. It includes the processor where all the work of the computer is carried out, plus input and output devices.
Web hosting is when a server holds a web page so it can be seen over the internet.
A web server is a computer with a full-time internet connection.
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) joins computers on different sites, cities, or countries.
Wi-Fi is a standard for sending and receiving 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 is a file operation in which a value is saved by copying it into a file in storage.