Computer Science GCSE

Computer Science GCSE glossary

457 key terms for Computer Science GCSE, A to Z, each linked to the topic pages that use it.

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A

Abstraction: Removing or hiding detail that is not needed for the current purpose, so only the essential features are modelled.OCR, Pearson Edexcel
Abstraction from hardware: High-level languages abstract away hardware details, which speeds up development and maintenance.OCR
Acceptable use policies: Written rules telling users what they may and may not do with an organisation's systems, so that human behaviour is controlled.Pearson Edexcel
Access control: Restricts who may use a system or which resources they may open, using logins, passwords and permission levels.Pearson Edexcel
Access point: A device that a device must associate with, which broadcasts a network name (SSID) and manages traffic.OCR
Accessing and updating fields by name: A field is accessed by name, such as student['name'], and updated by assigning a new value to that named field.OCR
Addressing at different layers: The transport layer adds port numbers, the internet layer adds source and destination IP addresses, and the link layer frames data with MAC addresses for the…Pearson Edexcel
Algorithmic thinking: Expressing a solution as a precise, ordered sequence of steps or rules that a computer could follow.OCR
ALU operations: Performs arithmetic such as addition and subtraction and logical operations such as AND, OR and comparisons.OCR
Amplitude: The height of the sound wave at the moment a sample is taken, which determines the binary value stored for that sample.Pearson Edexcel
Analogue to digital conversion: A microphone converts the sound wave into a varying analogue voltage, and an analogue-to-digital converter measures that voltage at regular intervals.OCR
Analysing, understanding and solving problems: Examining each part on its own, reasoning about a simpler model than reality, and sharing and testing work separately.Pearson Edexcel
AND: A binary operator that produces True only when both of its operands are True; if either operand is False, the result is False.OCR
Anti-malware: Software that scans files, memory and downloads for known malicious code and quarantines or removes threats, needing regular signature updates.OCR, Pearson Edexcel
Anticipating misuse: Thinking about every way a user could enter wrong, missing or harmful data, or use the system in an unintended order, and then building safeguards before…OCR
Appropriate design using parameters and return values: Passing needed data in as parameters, keeping working values local and returning results, using globals only for genuinely shared state.Pearson Edexcel
Arguments: The actual values supplied at the call, which are passed into the parameters.Pearson Edexcel
Arithmetic operators: Operators that compute values: addition combines, subtraction finds a difference, multiplication scales, division gives a quotient, modulus returns the…Pearson Edexcel
Arithmetic right shift: Moving every bit right but copying the original most significant bit into the new most significant bit, preserving the sign of a signed pattern.Pearson Edexcel
Array: Stores several values of the same data type under one identifier, with each value reached by an index.OCR
ASCII: In ASCII, each character is represented by a 7-bit or 8-bit code, for example A is 01000001.OCR
ASCII and Unicode: Examples of character sets, where ASCII is a small character set and Unicode is a much larger character set.OCR
Assembler: Translates assembly language mnemonics into machine code, matching mnemonics to the processor instruction set.OCR
Assembly language: Uses mnemonics that map almost one-to-one onto machine instructions and needs an assembler to translate it.Pearson Edexcel
assignment: An assignment replaces the value held by a variable after evaluating the expression on its right.OCR
Authentication: The process of confirming that a user is who they claim to be, usually by checking a username with a password, a PIN, a security token or biometric data.OCR, Pearson Edexcel

B

Backup: Copies files or whole drives to another location, either fully or incrementally, so data can be restored after loss.Pearson Edexcel
Backup and recovery procedures: Making copies of data, often to a separate location, and having a tested plan to restore systems and data after loss, damage or ransomware.Pearson Edexcel
Bandwidth: The amount of data that can be transferred per unit time, so a higher-bandwidth link can carry more data at once.OCR, Pearson Edexcel
Base 16 place value: A 2-digit hexadecimal number has place values 16¹ = 16 and 16⁰ = 1, so it represents values from 0 to 255.OCR, Pearson Edexcel
Binary: A format of patterns of 0s and 1s into which all data must be converted before a computer can process it.OCR
Binary addition with carry: Adding two positive binary patterns column by column from right to left, writing 0 and carrying 1 when 1 + 1 occurs.Pearson Edexcel
Binary inputs and outputs: Values of 0 or 1 that enter a gate and the value it produces.OCR
Binary multiples: Units of data storage that each increase by a factor of 1024, which is 2¹⁰, from the previous unit.Pearson Edexcel
Binary place value: An 8-bit binary number uses place values 128, 64, 32, 16, 8, 4, 2 and 1.OCR
Binary representation of data: Computers use binary to represent data such as numbers, text, sound and graphics, and program instructions.Pearson Edexcel
Binary representation of sound: The resulting stream of binary values is stored as a file, for example a WAV file.OCR
Binary search: Requires a sorted list, examines the middle item, then discards the half that cannot contain the target and repeats on the remaining half.OCR, Pearson Edexcel
Binary shift: A binary shift moves every bit in a binary pattern a stated number of places left or right.OCR
Bit: A single binary digit, either 0 or 1, and the smallest unit of data.OCR
Bit depth: The number of bits per sample; a greater depth gives more amplitude levels, so each sample is rounded less coarsely and quiet detail is preserved.OCR, Pearson Edexcel
Bitmap images: A grid of pixels, where each pixel is stored as a binary code for its colour.Pearson Edexcel
bits per second: The rate at which bits pass a point each second, used to measure network speed.Pearson Edexcel
Boolean: A data type that holds only True or False, used for conditions and flags.OCR
Boolean operators: Operators that work on truth values, each of which is either True or False, and let programs combine conditions.OCR
Boolean operators AND, OR and NOT: Operators that combine binary inputs to produce an output in a logic diagram.OCR
Boolean result: The true or false produced by a comparison, commonly used to control selection or iteration.Pearson Edexcel
Bootstrap and firmware: The program held in ROM, such as BIOS/UEFI firmware, that runs when a computer is switched on.OCR
Boundary data: Input at the exact limits of a valid range, used because logic errors frequently occur at these edges.OCR
Brute-force attacks: Trying many passwords or keys until one works.OCR
Bubble sort: Repeatedly compares adjacent items and swaps them when out of order, so large values bubble to the end, with passes repeated until no swaps occur.OCR, Pearson Edexcel
Built-in subprogram: A subprogram supplied by the language and called directly, such as print() or len().Pearson Edexcel
Bus topology: All nodes share a single backbone cable, with terminators at each end, and a break in the backbone can disrupt the whole network.Pearson Edexcel
Byte: A group of 8 bits that typically stores one character.OCR

C

Cache: Fast memory inside or close to the CPU that stores frequently used instructions and data, so a larger one reduces the need to access slower main memory.OCR
Cache hit: Occurs when requested data is found in the cache, which is much quicker than fetching it from main memory (RAM).OCR
Cache miss: Causes the CPU to fetch the required instruction or data from RAM and copy it into the cache for future use.OCR
Cache performance: Fast memory close to the CPU that stores frequently used instructions and data to reduce slower main memory access.OCR
Cache size: A key factor affecting CPU performance; a larger cache reduces the average time the CPU waits for data by storing more frequently used instructions.OCR
Capacity calculation: Total capacity is calculated by multiplying the number of items by the size of each item, then converting to a sensible unit.OCR
Carry out of the most significant bit: The extra most significant bit produced by a calculation, which is lost because the storage location cannot hold it.Pearson Edexcel
Casting: Converts a value from one type to another, for example int("25") turns the string "25" into the integer 25.OCR
Central management and access: One administrator can update software, set permissions and monitor use across all devices, which is faster and more consistent than visiting each machine.Pearson Edexcel
Character encoding: Computers store characters as binary codes so that text can be processed, compared and transmitted consistently.Pearson Edexcel
Character set: A character set provides the mapping between each binary code and a character.OCR
Ciphertext: The scrambled form of data that should remain unreadable without the correct key.OCR
Client: A computer that requests services or resources from a server in a client-server network.OCR
clock: Generates regular pulses that synchronise the fetch-decode-execute cycle.Pearson Edexcel
Clock speed: Measured in hertz (Hz), this is the number of clock cycles per second, and a higher value generally means more instructions can be processed per second.OCR
Close: Releases the connection and ensures buffered data is saved, and programs should close files after use, often using with open(...) as f: so closing happens…OCR
Cloud computing: The delivery of computing resources, such as storage, processing and software, over the Internet on demand, so users access them remotely rather than owning…OCR
Coarser resolution: A smaller number of bits gives coarser resolution, so values such as measurements or sound amplitudes are rounded to the nearest representable level.Pearson Edexcel
Code reuse: Calling the same named block whenever needed, which avoids duplicating code and lets one change fix every use.OCR
Colour depth: The number of bits used to represent each pixel's colour; a greater colour depth allows more distinct colours and improves colour accuracy.OCR, Pearson Edexcel
Combining conditions: Using AND, OR and NOT to join or invert Boolean expressions so one condition tests several facts.Pearson Edexcel
Comments: Brief comments explain purpose, assumptions or non-obvious decisions rather than repeating the code.Pearson Edexcel
Communication between users: Connections let users communicate through email, messaging and video calls.Pearson Edexcel
Compact representation of binary: Long binary strings become shorter and less error-prone to read and write, making hex a compact shorthand for binary.Pearson Edexcel
Comparative evaluation: Stating the advantage, then the matching disadvantage, and relating both to the characteristic named.OCR
Compiler: Translates a whole high-level program into machine code before any of it runs, producing an executable file that can be distributed and run later without the…OCR
Compiler behaviour: Translates the entire source program before any of it is executed, producing a machine code file, and reports errors together after translating the whole…Pearson Edexcel
Computational thinking: A set of problem-solving principles used before code is written.OCR
Computer Misuse Act 1990: Makes unauthorised access to computer material, unauthorised access with intent to commit further offences, and unauthorised modification of computer material…OCR
Computer start-up sequence: The CPU fetching and executing instructions from ROM to perform the power-on self-test, initialise hardware and load the operating system from secondary…OCR
Concatenation: Joining strings together, such as "Hello" + " " + "World", where both operands must be strings.OCR
Condition-controlled iteration: Repetition continues while or until a condition is tested, for example WHILE lives > 0 or REPEAT ...OCR
Constant: A value fixed when the program is written and not changed while it runs.Pearson Edexcel
control unit: Decodes instructions and directs the flow of data and control signals within the CPU.Pearson Edexcel
Control unit coordination: Decodes instructions and sends control signals that coordinate the other components and the timing of data movement.OCR
Copyright: Protects the fixed expression of original work such as source code, and arises automatically once the work is recorded.Pearson Edexcel
Copyright, Designs and Patents Act 1988: Protects original creative and design work, so copying software, music or images without permission can infringe copyright.OCR
Correcting: Finding and fixing logic errors such as wrong conditions, off-by-one loop bounds or misplaced statements, then amending them.OCR
Cost against performance: A trade-off where a device such as a solid-state drive costs more per gigabyte but gives fast access.OCR
Count-controlled iteration: The number of repetitions is known or calculated before the loop starts, for example FOR i = 1 TO 5.OCR
CPU access to instructions and data: Primary storage is the memory the CPU accesses directly while a program runs, because the CPU can only execute instructions and process data held in…OCR
CPU purpose: The processor that runs program instructions held in main memory, fetching each instruction, decoding it, carrying it out and storing any result.OCR
CPU working memory: Fast, directly accessible memory that temporarily holds data and instructions currently in use by the CPU.OCR
Creating: Writing a correct algorithm from a problem description, translating it into ordered steps using sequence, selection and iteration in the required notation.OCR
Cultural issues: Concerns about how technology shapes shared ways of life, for example streaming changing how music is consumed or social media altering language.OCR

D

Data compression: Reduces file size by removing redundancy, saving storage and speeding up transfer; it can be lossless or lossy.Pearson Edexcel
Data protection: Protecting data, for example by scrambling file contents with encryption software so files travel safely.OCR
Data Protection Act 2018: Controls how personal data is collected, stored and used, giving individuals rights such as access to their data and requiring organisations to keep it…OCR
Data transfer and backup between systems: Secondary storage allows data and programs to be transferred between different computer systems and backs up important files.OCR
Data validation: Checks that data entered into a program is sensible and complete before it is processed, though it cannot prove the data is true.Pearson Edexcel
Debugging: Finding why a program does not behave as intended, working out where the fault is, and fixing it by reading error messages, tracing variables and testing with…Pearson Edexcel
Decimal prefixes: OCR J277 uses decimal units: 1 kB = 1000 bytes, 1 MB = 1000 kB, 1 GB = 1000 MB, 1 TB = 1000 GB.OCR
Decode stage: The stage in which the control unit works out what the instruction means.OCR
Decomposition: Breaking a whole problem into successively smaller sub-problems, shown by reading downwards from the top box to lower levels.OCR, Pearson Edexcel
Dedicated function: The single job an embedded system carries out repeatedly and reliably, rather than being a general-purpose machine used for many tasks.OCR
Dedicated single function: The one job the processor, memory and input/output are chosen and fixed for, keeping the unit small, cheap, low-power and reliable.Pearson Edexcel
Defensive design: Writing programs that stay reliable and secure even when users behave unexpectedly or maliciously.OCR
Defragmentation: Moves parts of fragmented files into contiguous blocks on a magnetic hard drive, reducing read-head movement and improving access speed.OCR
Determining correct output from given data: Executing the algorithm exactly as written with the supplied data, then reading the final row to determine the output.Pearson Edexcel
Digit-to-letter mapping: Hexadecimal uses the digits 0–9 and the letters A–F, where A = 10, B = 11, C = 12, D = 13, E = 14 and F = 15.OCR
Discarded carry: The carry out of the eighth bit has a place value of 256, so discarding it makes the stored result incorrect, specifically 256 less than the true sum.OCR
Disk defragmentation: Rearranges fragmented files on a magnetic hard disk so blocks are contiguous, improving read speed.Pearson Edexcel
Domain name resolution: A DNS server translates the human-readable domain name into the numeric IP address that identifies the destination server.OCR
Duration: How long the sound lasts; increasing it increases the number of samples stored, so the file becomes larger, but it does not affect the playback quality.OCR

E

Editor: The facility where source code is written, usually with features such as line numbering, syntax highlighting and automatic indentation.OCR
Efficiency of algorithms: Merge sort is more efficient on large lists, while bubble and insertion sort are simple and suit small lists.OCR
Efficient use of finite storage: Compression reduces the number of bits needed to store a file, so more files fit on a given device because storage capacity is finite.OCR
Embedded system: A computer built into a larger device to carry out one dedicated job rather than being a general-purpose machine.Pearson Edexcel
Encapsulation: As data passes down the stack, each layer adds its own header.OCR
Encapsulation and de-encapsulation: Each layer adds its own header as data moves down the stack, and de-encapsulation removes headers as data moves up the receiver's stack.Pearson Edexcel
Encode: To encode text, each character is converted to its binary code and the codes are stored in sequence.OCR
Encryption: Scrambles data using a key so that intercepted or stolen data is unreadable without the correct key, protecting data in transit and at rest.OCR, Pearson Edexcel
Encryption software: Uses an algorithm and a key to convert plaintext into ciphertext so data cannot be understood if intercepted.OCR
Environmental issues: Concerns covering energy use in data centres, mining materials for batteries such as lithium and cobalt, and electronic waste.OCR
Equality testing versus assignment: Two equals signs test equality, while a single equals sign assigns a value.Pearson Edexcel
Error diagnostics: Facilities that help the programmer find and fix mistakes by flagging syntax errors, showing messages and sometimes suggesting corrections.OCR
Error reporting and debugging: A compiler reports all errors together after compilation, whereas an interpreter stops and reports the first error it encounters, making debugging easier.OCR
Errors and execution speed: Compiled code generally executes faster because translation is completed in advance, while interpreted code is convenient during development because errors…Pearson Edexcel
Estimation and conversion: Convert between units by dividing by 1000 to move to a larger decimal unit, and always state the final unit.OCR
Ethernet: A family of protocols and standards used for wired local area networks, defining how devices format and transmit frames over a shared medium.OCR
Ethical hacking: Uses the same techniques as malicious hacking but with permission and within legal and contractual limits.Pearson Edexcel
Ethical issues: Questions about what is right or fair, such as whether a company should sell personal data or a self-driving car should prioritise one life over another.OCR
Evaluating AND, OR and NOT operators: Working through each row using the operator definitions to find the output, adding intermediate columns for sub-expressions to prevent errors.OCR
Evaluating combined logic circuits: Tracing inputs through gates in order, working left to right and writing the intermediate value on each connecting line.OCR
Everyday control devices: Products such as washing machines, microwave ovens, central heating thermostats, digital cameras, fitness trackers, traffic lights, pacemakers and domestic…OCR
Examples of LANs and WANs in everyday life: A school with computers in several rooms linked by its own switches and cabling is a LAN, and the internet is the largest WAN.OCR
Execute stage: The stage in which the control unit sends control signals, the ALU may calculate, and results are written back to registers or memory.OCR
Execution speed versus development speed: Compilers give fast execution but slow development because each change needs a full recompile, while interpreters give slower execution but allow quick testing.OCR
Exponentiation: Raises a base to a power, for example side ** 2 for a square's area and side ** 3 for a cube's volume.Pearson Edexcel

F

Factors limiting CPU performance: Performance gains are limited by cache misses, memory bandwidth, thermal limits and how well software uses multiple cores.OCR
Faster data transmission: Smaller files transmit faster over a network because fewer bits must be sent.OCR
Fetch stage: The stage in which the address in the program counter is copied to the memory address register and the instruction at that address is transferred to the…OCR
File formats and properties: Details such as file format and creation date that metadata may include to describe a file.OCR
File management: Organises how files and folders are stored, named, located, moved, copied and deleted, and controls access rights.Pearson Edexcel
File repair: Scans a damaged file's structure and rebuilds what it can, so a corrupted document may open again.Pearson Edexcel
File size: In bits it is calculated as sample rate × bit depth × duration in seconds × number of channels, and doubling any of these three factors roughly doubles it.OCR
File size and quality trade-offs: A higher sample rate and bit depth capture the wave more accurately but create a larger file.OCR
File size calculation: Uncompressed file size in bits is calculated as width × height × colour depth, then divided by 8 for bytes and by 1000 for kB and MB.OCR, Pearson Edexcel
File-size expression: A calculation that multiplies the number of items by the bits or bytes required per item.Pearson Edexcel
Final or terminal testing: Testing carried out once the whole program is complete and integrated, checking the system as a whole against the original requirements.OCR
Finding defects: Testing aims to uncover logic errors and defects before the software is released to users.OCR
Firewall: Monitors and filters incoming and outgoing network traffic against a set of rules, blocking unauthorised connections.OCR, Pearson Edexcel
Firmware in ROM: The program stored in ROM so the system starts instantly and cannot easily be changed.OCR
Firmware in ROM or flash memory: The program usually stored in ROM or flash memory that runs automatically when the device is switched on, so the user does not install software.Pearson Edexcel
Fixed firmware: The software an embedded computer runs to perform one control job, processing the input and producing the control output.OCR
Fixed-length codes: Because the code length is fixed at 7 bits, every character takes the same space, and codes can be sorted into a standard order.Pearson Edexcel
Fixed-width storage: A storage location with a set number of bits, so a value needing more bits than it provides cannot be held.Pearson Edexcel
Format check: Confirms input matches an expected pattern, such as a postcode or date.OCR
FROM: Names the table, copying table and column names exactly as given in the question.OCR
Full mesh: A mesh in which every device connects to every other device.OCR
Function: A subprogram that must return a value to the caller, so its call can be used inside an expression.Pearson Edexcel
Functions versus procedures: A procedure performs an action and may display or update data without returning a value, whereas a function performs a calculation and returns a value to the…OCR

G

Global versus local access: A global is declared in the main program and accessible throughout, whereas a local is created inside a subprogram and code outside cannot see it.Pearson Edexcel

H

Hardware control and performance: Low-level languages allow precise control over hardware resources such as registers and memory addresses, which can improve execution speed or reduce program…OCR
Hex digit values: The digits 0-9 and A-F, where A = 10, B = 11, C = 12, D = 13, E = 14 and F = 15.OCR
Hexadecimal: Base 16, where each digit represents a group of four binary bits.OCR
Hierarchy: The arrangement of boxes by level, where each lower level shows a decomposition of the box above it and boxes on the same level are sibling sub-tasks.OCR
High-level language: Uses readable statements, data structures and abstraction, so programs are quicker to develop, easier to maintain and usually portable, though a translator is…Pearson Edexcel
Hosting and service provision: Storing a website or service on a server that is reachable over the Internet, which may be owned locally or rented from a provider.OCR
HTTPS: HTTP carried over an encrypted connection, commonly using TLS, so data such as login details cannot easily be read in transit.OCR, Pearson Edexcel
Human readability and maintainability: High-level languages use English-like keywords and abstractions such as variables, loops and functions, making programs easier for humans to read, write and…OCR

I

ID and password: Details collected from the user, where the program searches stored records for the supplied ID and compares the stored password with the one entered.Pearson Edexcel
Image quality: Improved by higher resolution, which allows finer detail, or greater colour depth, which improves colour accuracy, but each increases file size.OCR
IMAP: Keeps messages on the server so they can be synchronised across devices, unlike downloading to one device.OCR, Pearson Edexcel
Immutability: Operations return a new string rather than changing the original, so strings cannot be changed in place.OCR
Inclusive comparisons: Comparisons that combine an angle bracket with an equals sign, so the boundary value is also accepted.Pearson Edexcel
Indentation: Shows which statements sit inside loops, selections and sub programs, making the control flow visible.OCR, Pearson Edexcel
Index: The value used to reach an element in an array, commonly starting at 0 so the last index is size − 1.OCR
Indexing: Position of a character in a string, usually starting at 0, so the first character is at position 0.OCR
Initialisation: Giving a variable its first value, while assignment later replaces that value.Pearson Edexcel
input and output: Input brings data into the program, often from a user or sensor, while output communicates a result through a screen, file or device.OCR
Input devices: Hardware that converts data such as text, images, sound and instructions into binary, for example a keyboard producing a character code.OCR
Input validation: Checks that data entered by a user is sensible, complete and in the expected format before the program processes it.OCR
Input–process–output: The pattern used to structure an answer, identifying the input, the processing and the output for a named example to show understanding of the concept.OCR
Inputs: The data or signals that enter the system, such as a customer's age typed into a ticket machine.OCR
Insertion sort: Builds a sorted section at the start by taking the next item and inserting it into the correct position among those already sorted, shifting larger items right.OCR
Integer: A data type that holds whole numbers such as 42 or -7, used for counting and exact arithmetic.OCR
Integer division: Discards the fractional part, giving how many whole times one number fits into another.Pearson Edexcel
integer division and modulus: Integer division (DIV) returns only the whole-number quotient, while modulus (MOD) returns the remainder.OCR
Interaction with sensors and actuators: Reacting to inputs from sensors and driving parts such as a motor and valve in the physical world.OCR
Interference: A factor that can reduce wireless performance, along with distance from the access point and physical obstacles.OCR
Interoperability and compatibility: The ability of equipment from different manufacturers to communicate, which standards improve and which makes network behaviour predictable.OCR
Interpretation of raw data: Using metadata so that software can make sense of raw data, which may otherwise be meaningless, such as knowing how many pixels wide an image is.OCR
Interpreter: Translates and executes source code line by line, which helps with debugging because errors are reported as they are encountered.OCR
Interpreter behaviour: Translates and executes the source one statement at a time, stopping when it reaches an error, and produces no standalone machine code file.Pearson Edexcel
Interpreting: Reading an algorithm and stating its purpose or output, tracing it with sample data to state its behaviour, including edge cases.OCR
Invalid or erroneous data: Input that does not meet the stated rule and should be rejected by the program.OCR
IP address: A logical address, often assigned by a DHCP server, which can change when a device joins a new network and which routers use to forward packets.OCR
IP addressing: An IP address identifies a device or interface on a network so data reaches the right destination.Pearson Edexcel
IPv⁴: A 128-bit address written as eight groups of hexadecimal digits separated by colons, created because IPv⁴ addresses are running out.OCR
Iterative and terminal testing: Iterative testing occurs during development to check individual modules, while terminal testing evaluates the finished program.OCR
Iterative testing: Repeated testing carried out as each module or feature is written, where the programmer runs the code, checks outputs against expected results, fixes defects…OCR

K

Key: Controls the scrambling and unscrambling, and is required to encrypt and decrypt.OCR
kilobit, megabit and gigabit: Prefixes that scale by 1000, so 1 megabit per second is 1000 kilobit per second.Pearson Edexcel
Kilobyte: A unit of 1,000 bytes, or 1 KB, the first step above the byte in the ladder of units.OCR

L

LAN: Covers a small area such as one building or campus, for example a school where computers, printers and a file server are linked by the school's own cabling…OCR, Pearson Edexcel
Latency: The delay before data starts to arrive, and it affects how responsive a connection feels.Pearson Edexcel
Layered communication: The TCP/IP model splits network communication into four layers, each with a distinct job, working in sequence as data moves down the sender's stack and up the…Pearson Edexcel
Layering: Splits network communication into separate jobs so each layer handles one concern and offers services to the layer above.OCR
Leading zeros: Zeros added to pad the leftmost nibble when the binary integer does not contain a multiple of four bits.OCR
Least significant bit: The rightmost bit, where column-by-column binary addition starts, moving leftwards while processing carries.OCR
Legal issues: Issues that arise when behaviour is governed by law, such as handling personal data under the Data Protection Act 2018.OCR
Length check: Confirms a string has an allowed number of characters, such as a username between 4 and 12 characters.Pearson Edexcel
Library subprogram: A subprogram that must be imported before use, for example importing a maths module and then calling its square-root function.Pearson Edexcel
Licencing: The owner granting permission to use software under stated conditions, for example single-user, site or open-source licences.Pearson Edexcel
Lifetime of local variables: Created when the subprogram is called and ceasing to exist when it ends, so it no longer exists outside its subprogram.Pearson Edexcel
Linear search: Checks each item from the start of a list in turn until the target is found or the list ends, so it works on unsorted data.OCR, Pearson Edexcel
Logic error: Code is syntactically valid and runs, but produces an incorrect result because the algorithm's steps or conditions are wrong.OCR, Pearson Edexcel
Logic errors: Errors that let the program run but produce wrong results, such as using addition where subtraction is needed or a condition that is never true.Pearson Edexcel
Logic gate symbols and functions: Each gate has a distinctive symbol, and AND requires all inputs to be 1, OR requires at least one input to be 1, and NOT inverts its single input.OCR
Logical left shift: Moving every bit one place left, putting 0 in the least significant bit, and multiplying the unsigned value by 2.Pearson Edexcel
Logical operators: Operators that combine or invert Boolean results: AND is true only when both inputs are true, OR is true when at least one is true, and NOT reverses a single…Pearson Edexcel
Logical right shift: Moving every bit one place right, putting 0 in the most significant bit, and dividing the unsigned value by 2, discarding any remainder.Pearson Edexcel
Lookup: Searches stored records for the supplied ID and retrieves the associated stored password or credential.Pearson Edexcel
Loss of precision: A right shift causes a loss of precision, discarding any bits shifted past the right-hand end and losing fractional parts.OCR
Lossless compression: Reduces file size without losing any data, so the original can be restored exactly.OCR
Lossless compression and exact reconstruction: Reduces file size while allowing the original data to be reconstructed exactly, so it suits text, spreadsheets, source code and archives.Pearson Edexcel
Lossless methods: Find patterns and store them more efficiently, often using dictionary or run-length techniques.OCR
Lossy compression: Permanently removes some data to achieve a smaller file, used where approximate reproduction is acceptable.OCR
Lossy compression and permanent data loss: Permanently discards some detail that humans are less likely to notice, giving much smaller files for images, audio and video, but the original cannot be…Pearson Edexcel
Low cost and low power: Characteristics of embedded systems that make the system cheap and dependable, with unnecessary hardware and software stripped away.OCR
Low-power device connectivity: A design for low power consumption that suits battery-powered devices such as wireless earbuds, keyboards, fitness trackers and car systems.OCR

M

MAC address: A physical address burned into the network interface card by the manufacturer, fixed for the life of the interface and used within a local network to identify…OCR
MAC addressing: Used by Ethernet to identify the source and destination network interface cards on the network.OCR
Machine code: Binary instructions executed directly by the CPU, forming the lowest level of language and needing no translation.Pearson Edexcel
Magnetic storage: Uses magnetised areas on a spinning platter read by a moving head, for example a hard disk drive (HDD).OCR
magnetic storage method: Stores data by magnetising tiny areas on a spinning platter, with read/write heads detecting or changing the magnetic state.Pearson Edexcel
Maintainability: Means another programmer can read, understand and safely change a program later.OCR
Malware: Software written to harm or exploit, including viruses that attach to files, worms that self-replicate across networks, trojans disguised as useful programs,…OCR, Pearson Edexcel
MAR (Memory Address Register): Holds the address of the memory location currently being read from or written to, sending that address along the address bus.OCR
Matching compression method to file type: Choosing a method depends on whether exact recovery matters, so a text document needs lossless while a photograph for a web page may accept lossy.Pearson Edexcel
Matching technology to user need: Identifying the demands of the task before selecting a device, then comparing candidate media against capacity, speed, portability, durability, reliability…OCR
MDR (Memory Data Register): Holds the data or instruction fetched from memory via the data bus, or the data to be written to memory.OCR
Meaningful identifiers: Variable, constant and subroutine names describe their role, such as markTotal instead of t.Pearson Edexcel
Meeting requirements: Testing confirms that a program functions as intended and meets its original requirements.OCR
Memory management: Allocates RAM to programs, keeps track of free and used areas, and prevents programs overwriting each other.OCR
Merge sort: Splits the list into single items, then repeatedly merges pairs of sorted sublists by comparing their front items until one sorted list remains.OCR, Pearson Edexcel
Mesh topology: Nodes connect to multiple other nodes, and a full mesh links every node directly to every other node, giving high resilience but requiring many connections.OCR, Pearson Edexcel
Metadata: Data about data that describes a file's content, format, origin, and properties so that software and users can interpret and manage it.OCR
Modelling aspects of the real world: Using decomposition and abstraction so that only the essential features of a real-world situation are represented.Pearson Edexcel
Modulus: Returns the remainder, which is useful for testing divisibility or wrapping values.Pearson Edexcel
Multiplication and division by powers of two: A left shift by n places multiplies the value by 2ⁿ, while a right shift by n places divides the value by 2ⁿ, discarding any bits shifted past the right-hand…OCR
Multitasking: Allows several processes to appear to run at once by sharing processor time, often through rapid switching.OCR

N

Named fields and data types: Each field in a record has a name and a data type, such as name (string), age (integer) and average (real).OCR
Naming conventions: Give variables and sub programs meaningful names, so their purpose is obvious.OCR
Need for compression: Compression reduces the number of bits used to store or transmit data, saving storage space and reducing transmission time and bandwidth use.Pearson Edexcel
Network classification by scale: Networks are classified by the area they cover and who controls them, so the difference is one of scale and ownership rather than purpose.Pearson Edexcel
Network of networks: Many independently owned networks are joined so that any device can exchange data with any other.Pearson Edexcel
Network topology: The arrangement of devices and connections in a network.OCR
Networks and interconnection: The Internet is a worldwide collection of computer networks, not a single network, with independent LANs and WANs interconnecting through routers.OCR
Nibble: A group of 4 bits, useful because one hexadecimal digit represents exactly one nibble.OCR, Pearson Edexcel
Nibble-to-hex-digit mapping: One hex digit maps exactly to four binary bits, so each nibble is replaced with its hex digit.Pearson Edexcel
NIC: Gives each computer a network interface and a MAC address so that a stand-alone computer can connect to a network.OCR
Non-volatile data storage: Storage that holds data and programs permanently, unlike RAM, which is volatile.OCR
Non-volatile memory: Memory that retains its contents when the power is removed, which is true of ROM.OCR
Normal data: Valid, typical input that lies well inside the accepted range and should produce the expected result.OCR
NOT: A unary operator that negates a single Boolean value, turning True into False and False into True.OCR
Number bases: Denary is base 10, using digits 0–9, while binary is base 2, using only 0 and 1.OCR
Number of cores: More cores allow multiple instructions or programs to be processed simultaneously, which can improve performance for tasks that can be parallelised.OCR
Number of users: More simultaneous users means each gets less because bandwidth is divided between them.OCR
Numbers, text, sound and graphics: These are the data types that computers represent using binary.Pearson Edexcel

O

Open: Creates a connection between the program and a named file on secondary storage, with the chosen mode determining whether the program can read, overwrite or…OCR
Operands: Every operator needs a value on each side, so a complete expression has both present.Pearson Edexcel
Operating system and firmware start-up: Primary storage holds the operating system in use and the BIOS/firmware needed at start-up.OCR
operator precedence: Standard rules, given as BODMAS or BIDMAS, applied in order: brackets first, then exponentiation, then division and multiplication, and finally addition and…OCR
Operator precedence and grouping: When operators are combined, evaluate NOT first, then AND, then OR, unless brackets change the order.OCR
Operator selection: Choosing the correct operator for the intended logic and placing it between valid Boolean expressions.Pearson Edexcel
Optical storage: Uses a laser to read pits and lands on a reflective disc, for example CD, DVD and Blu-ray.OCR
optical storage method: Stores data as pits and lands on a reflective surface, where a laser beam is reflected differently and the pattern is interpreted as binary.Pearson Edexcel
Output devices: Devices such as monitors, speakers or printers that convert binary results back into a human-readable form.OCR
Outputs: The results presented or stored, such as displaying the ticket price or writing a record to a file.OCR
Overflow: Occurs when a result exceeds the largest storable value, so the extra carry has nowhere to go and the result cannot be stored correctly.OCR, Pearson Edexcel
Overflow error: Occurs when a carry is generated out of the most significant bit (the 128s column) and, with no ninth bit to store it, is discarded.OCR
Ownership and infrastructure: A LAN usually uses owned cabling, switches and wireless access points, while a WAN depends on external links and routers.Pearson Edexcel
Ownership and management of network infrastructure: LAN hardware is typically owned and managed by the organisation, whereas WAN infrastructure is usually owned by third parties such as telecom providers.OCR

P

Packet forwarding by routers: Routers read the destination address and forward each packet along the best available path, hop by hop, until it arrives.Pearson Edexcel
Page file or swap file: A reserved area of secondary storage where the operating system moves pages of data that are not currently being used when RAM becomes full.OCR
Pairing and device security: The process of establishing a trusted connection between devices, often involving a shared passcode or confirmation, which helps prevent unwanted connections.OCR
Parameters: The named inputs declared in the subprogram definition, which may be zero or more for both functions and procedures.Pearson Edexcel
Parameters and arguments: Parameters are placeholders in the definition, while arguments are the actual values supplied when the sub program is called.OCR
Partial mesh: Some nodes have more than one path to other nodes, balancing resilience against cost.Pearson Edexcel
Patents: Protects a new, inventive technical process or device and must be applied for and granted before it can be enforced.Pearson Edexcel
Peer: A computer with an equal role that can act as both client and server, sharing resources directly with others.OCR
Peer-to-peer network: A network where every computer has an equal role and no central server controls the network.OCR
Penetration testing: Simulates attacks to find weaknesses before criminals do, allowing them to be fixed before real attackers exploit them.OCR, Pearson Edexcel
Performance and security trade-offs: Wireless gives mobility and easy installation but can suffer interference, weaker security and variable bandwidth.OCR
Peripheral management: Uses device drivers to send data to and receive data from input, output and storage devices such as keyboards, printers and disks.OCR, Pearson Edexcel
Personal area networks: A small network formed by devices connected over a short range, such as a piconet in which one device is master and others are slaves.OCR
Physical and logical network specifications: Standards cover physical properties such as Ethernet cable connectors and Wi-Fi radio frequencies, and logical properties such as data formats and the rules…OCR
Pixel: A bitmap image is a grid of pixels, and each pixel stores one colour value as a binary code.OCR
Place value in base 2: The values 128, 64, 32, 16, 8, 4, 2 and 1 used for unsigned conversion, where a bit set to 1 adds its place value.Pearson Edexcel
Plaintext: The original data that encryption scrambles into ciphertext.OCR
POP: Downloads email to a single device and may delete it from the server.OCR
Portability across platforms: High-level languages are generally portable because a translator or virtual machine adapts the same source code to different hardware.OCR
Portable: Describes high-level code that can generally be moved across machines, though it must still be translated before execution.Pearson Edexcel
Powers of two and state counts: The number of distinct states for a pattern of n bits is 2ⁿ, found by raising 2 to the power of the bit length.Pearson Edexcel
Practical handling of large media files: Streaming and downloading become more practical when file sizes are smaller, and the need applies to text, images, sound and video.OCR
Presence check: Confirms a field is not empty, for example rejecting a blank email box.OCR, Pearson Edexcel
Primary storage: Fast storage that the CPU can access directly, with RAM acting as this type of storage.OCR
Primary storage roles: Both RAM and ROM are primary storage directly accessible by the CPU, but they serve different roles.OCR
Problem solving with logic: Truth tables show exactly when a system outputs True, which helps design logic circuits, test program conditions and check whether two expressions are…OCR
Procedure: A subprogram that does not return a value and is called as a standalone statement.Pearson Edexcel
Process management: Decides which programs or processes get processor time, schedules them, shares memory between them and closes them when finished.Pearson Edexcel
Processes: The operations, calculations or decisions performed on the data, such as checking whether the age is below 16 and calculating the price.OCR
Program Counter: Holds the address of the next instruction; during the fetch stage its value is copied to the MAR and it is then incremented.OCR
Program instructions as binary: Computers use binary to represent program instructions as well as data.Pearson Edexcel
Program testing: Testing the program with inputs that make each combined condition true and false.Pearson Edexcel
Protocol: An agreed set of rules that lets devices communicate, needed for reliable, standardised exchange between different hardware and software.Pearson Edexcel
Pseudorandomness: Values that look random but are produced by a deterministic algorithm, so they are predictable if the seed and algorithm are known.OCR
Purpose of networking: Computers are connected so they can exchange data and share resources, because sharing is cheaper and more flexible than giving every user a separate copy of…Pearson Edexcel

R

RAM: Main memory that is directly accessible by the CPU and is volatile, losing contents when power is removed.Pearson Edexcel
Range: How far a signal can travel while remaining usable, limiting where wireless devices can operate.Pearson Edexcel
Range and bounds: The limits of the values produced, which are language-specific; in OCR Reference Language random(x, y) returns an integer from x to y inclusive.OCR
Range and overflow: In 8-bit two's complement the range is −128 to +127, and overflow occurs when a result falls outside the representable range.Pearson Edexcel
Range check: Confirms a number or ordered value lies between limits, such as a test score from 0 to 100.OCR, Pearson Edexcel
Range of unsigned integers from 0 to 2ⁿ − 1: With n bits there are 2ⁿ different patterns, so the range of unsigned integers runs from 0 to 2ⁿ − 1.Pearson Edexcel
Read: Retrieves data from an opened file into program variables, where read() returns the whole remaining content, readline() returns one line and readlines()…OCR
Read/write access: RAM can be read from and written to, while ROM is normally read-only and not changed by ordinary programs.OCR
Real: A data type that holds decimals such as 3.14 or -0.5, for numbers with fractional parts.OCR
Record: A data structure that stores related fields about one entity, with each field having a name and a data type.OCR
Reduced bandwidth and cost: Reduced bandwidth use lowers congestion and can reduce data-transfer costs, which matters when many users share a connection.OCR
Refining: Improving an already working algorithm, for example by removing repeated code or handling invalid input.OCR
Refining an algorithm: Improving an algorithm's design, such as fixing errors, handling unexpected inputs robustly, or increasing efficiency, by identifying the specific weakness…OCR
Register storage: Very small, very fast storage locations inside the CPU, each holding a current value during processing.OCR
Regression checking: Checking after a fix that a change has not introduced new faults elsewhere, as part of iterative testing.OCR
Relational operators: Operators that compare values and produce a Boolean result of true or false, including equal to, less than, greater than, not equal to, less than or equal to…Pearson Edexcel
Reliable data transmission: With TCP, the transport layer adds sequence numbers and checksums so lost or corrupted segments can be resent.Pearson Edexcel
Resolution: The number of pixels in an image, often expressed as width × height; higher resolution means more pixels and allows finer detail.OCR, Pearson Edexcel
Resource sharing: A school office can send a document to a networked printer instead of buying one printer per desk, and staff can open the same shared folder rather than…Pearson Edexcel
Reuse: Calling the same subprogram many times instead of rewriting the same code, which shortens programs and reduces the chance of inconsistent errors.Pearson Edexcel
Reversibility of conversion methods: A conversion is checked by reversing the method, such as converting CA₁₆ back to 202 to confirm the answer.OCR
Robustness: Testing verifies that a program can handle unexpected actions without crashing.OCR
role of secondary storage: Provides non-volatile, long-term storage for data and programs when the computer is switched off, and is not directly accessed by the CPU.Pearson Edexcel
Rounding or truncation: Happens when a value cannot be represented exactly, such as a fraction stored with a limited number of fractional bits.Pearson Edexcel
Router: Connects the LAN to other networks, such as the internet, and directs packets between them.OCR
Routing between separate networks: A router connects separate networks, for example a home network to an internet service provider.Pearson Edexcel
Run-time environment: The facility that allows the program to be executed and tested from inside the IDE, often with a debugger for stepping through code and inspecting variables.OCR
Runtime error: The fault occurs during execution, for example division by zero, an out-of-range array index, or invalid type conversion.OCR, Pearson Edexcel
Runtime errors: Errors that occur while the program is running, for example dividing by zero or accessing an index outside the bounds of a list.Pearson Edexcel

S

Sample interval: The time between one sample and the next, where a shorter interval means more samples are taken in each second.Pearson Edexcel
Sample rate: How many samples are taken each second, measured in hertz (Hz); a higher rate captures rapid changes in the wave more accurately.OCR, Pearson Edexcel
Sampling and quantisation: Each measurement is a sample, and each sample is rounded to the nearest available level.OCR
Scope of variables: A global variable can be read or changed by any subprogram, while a local variable is accessible only within the subprogram it is declared in.Pearson Edexcel
Searching within data structures: A searching algorithm locates a target value within a data structure and reports its position or confirms absence.OCR
Searching, sorting, and management of digital assets: Ways metadata is used, including searching, sorting, copyright tracking, and automatic processing.OCR
Secondary storage characteristics: The properties compared when choosing media: capacity, speed, portability, durability, reliability and cost.OCR
SELECT: Names the fields to return, and uses * only when every column is wanted.OCR
Selection: A condition is evaluated and exactly one branch runs, for example IF ...OCR, Pearson Edexcel
Sensors and actuators: The inputs a controller reads, such as water-level and temperature sensors, and the outputs it drives, such as valves and a motor.OCR
Sequence: Statements execute in the order written, so swapping two lines can change the result.OCR
Server: A powerful computer that stores data, manages user accounts, applies security and responds to requests.OCR
Short-range wireless communication: A technology that lets devices exchange data directly over a short distance, typically only a few metres.OCR
Sign bit and place value: The most significant bit indicates the sign, and its place value is negative, which is why 10000000 represents −128.Pearson Edexcel
Signed 8-bit range -128 to +127: The range of values represented by 8-bit patterns interpreted as signed, running from -128 to +127.Pearson Edexcel
Simulation and games: Uses of random number generation such as simulating a dice roll with a random integer from 1 to 6, or selecting a random item from an array.OCR
Single-bit rules: The rules for adding one bit to one bit: 0+0=0, 0+1=1, 1+0=1, 1+1=10₂ (write 0, carry 1), and 1+1+1=11₂ (write 1, carry 1).OCR
Slicing: Extracting a substring, for example "Computer"[0:3] giving "Com".OCR
Social engineering: Manipulating people, for example through phishing emails or messages that trick users into revealing credentials or opening attachments, exploiting people as…OCR, Pearson Edexcel
Software licences: Set the terms of use: proprietary licences restrict copying, modification and redistribution, while open source licences allow users to view, modify and share…OCR
solid state storage method: Stores data in flash memory chips using electrical charge in floating-gate transistors, with no moving parts.Pearson Edexcel
Solid-state storage: Uses flash memory with no moving parts, for example an SSD, USB flash drive or SD card.OCR
Speed and performance: Primary storage is much faster than secondary storage, and too little memory forces swapping to slower secondary storage, reducing performance.OCR
SQL injection: Inserting malicious SQL through unvalidated input to read or alter a database.OCR
SSID: A network name broadcast by an access point.OCR
Standard interfaces: Between layers, these let different vendors' hardware and software interoperate, which is why the internet works across mixed equipment.OCR
Standards: Agreed, documented specifications that allow hardware and software from different manufacturers to interoperate on a network.OCR
Star topology: Each node connects to a central switch or hub, so a single node or cable failure affects only that node, but the central device is a single point of failure.OCR, Pearson Edexcel
Start-up and firmware: ROM stores fixed instructions such as the bootstrap/BIOS program used at start-up, running the power-on self-test and locating the boot loader.OCR
Step-by-step execution of algorithms: Working through each statement in order, updating every variable as its value changes, and respecting sequence, selection and iteration.Pearson Edexcel
Storage characteristics: The features of capacity, speed, portability, durability, reliability and cost that every storage device balances.OCR
Storage management: Freeing storage space, for example by compressing or removing redundant files when a laptop is full.OCR
Storing multiple records in a collection: Many records can be held in a list or file, then looped through to search, calculate or display.OCR
Structure diagram: A top-down design tool that breaks a whole problem into successively smaller sub-problems until each part is simple enough to code as a module.OCR
Structured programming: Breaking a program into named, self-contained blocks, each with one clear job, so programs are easier to read, test, debug and reuse.OCR
Sub programs: Break a large task into named modules, so each part can be tested and edited without disturbing the rest.OCR
Subprogram: A named block of code that performs one task and can be called whenever that task is needed.Pearson Edexcel
Suitability for purpose: Explaining why a characteristic matters in context, for example portability for a device carried daily.OCR
Swapping: The operating system moving pages or blocks of data between RAM and a page file or swap file on secondary storage, in both directions.OCR
Switch: Connects devices within one LAN and forwards frames only to the intended port rather than broadcasting to all.OCR
Syntax error: An error that breaks the rules of the language, such as a missing bracket or a misspelled keyword, and prevents the program running at all.OCR, Pearson Edexcel
Syntax errors: Errors where the code breaks the rules of the language, so the program will not run, such as a missing closing bracket or a misspelled keyword.OCR, Pearson Edexcel
System maintenance: Maintenance or protective tasks performed on a computer system, separate from the core operating system functions.OCR
Systematic enumeration of input combinations: Listing inputs in a consistent order such as 00, 01, 10, 11, where two inputs give four rows and three inputs give eight rows, following 2ⁿ combinations.OCR

T

TCP/IP: The foundational suite in which IP handles addressing and routing, while TCP provides reliable, ordered delivery by segmenting data and checking for errors.OCR, Pearson Edexcel
Teamwork: Supported because teams can divide work by assigning different subprograms to different programmers.Pearson Edexcel
Test data: Used with expected output to identify logic errors by comparing it with actual output.OCR
Test plan: Uses normal, boundary, invalid, and erroneous data.OCR
Testing and debugging: Easier because each subprogram can be checked in isolation, and a fault found can be fixed once inside the subprogram rather than in every copy.Pearson Edexcel
Testing logical equivalence: Using truth tables to test if two logical expressions are equivalent by comparing whether they produce identical outputs for all input combinations.OCR
The role of agreed rules in networking: Without agreed rules, devices could use incompatible signalling or data formats and fail to communicate, while standards simplify troubleshooting.OCR
time = file size ÷ transmission rate: The relationship linking file size, transmission rate and time, which can be rearranged to find file size or rate.Pearson Edexcel
Trace: A useful method of following a small input by hand and comparing the result with the expected result to find an error.OCR
Trace table: Used to trace the algorithm, record each variable after every step, and find the first step where a value differs from the expected value.Pearson Edexcel
Trace tables: Support dry runs to track variable changes and locate logic errors, which produce incorrect results.OCR
Trade-offs in system design: Accepting a disadvantage for an advantage, such as lower cost against slower speed.OCR
Trademarks: Protects brand identity such as a name, logo or slogan that distinguishes a product or company.Pearson Edexcel
Translation of high-level code: A compiler translates the whole high-level source program in one go, whereas an interpreter translates and executes it one statement at a time.Pearson Edexcel
Translator: Converts source code written by a programmer into a form that a computer can execute, bridging human-readable code and binary instructions.OCR
Translators: Facilities, such as compilers or interpreters, that convert the source code into a form the computer can execute.OCR
Transmission media: The path that carries the signals, such as copper cable using electrical signals, fibre optic cable using light, or wireless using radio waves.OCR
Truncated stored result: The incorrect value kept when only the low bits are stored and the extra most significant bits are discarded.Pearson Edexcel
Truth table: Lists every combination of input values and the output for each combination.Pearson Edexcel
Truth table construction: A table lists every possible combination of input values and the resulting output for a Boolean expression, with a column for each intermediate operation…OCR
Truth tables: A table that lists every possible combination of binary inputs and the resulting output for a Boolean expression or logic diagram.OCR
Two states: The condition of a computer's electrical signals being either on or off, which is why all data must be represented as binary patterns of 0s and 1s.OCR
Two-digit range 0 to 255: A 2-digit hexadecimal number has place values 16 and 1, so it represents values from 0 to 255.OCR
Two's complement representation: A signed 8-bit pattern in which the leftmost bit has place value -128 and the other bits keep 64, 32, 16, 8, 4, 2 and 1.Pearson Edexcel
Two's complement signed representation: The most significant bit is reserved as a sign indicator, where 0 means non-negative and 1 means negative.Pearson Edexcel

U

Unit conversion: Dividing or multiplying by the correct power of 1024, keeping the direction correct and stating the unit.Pearson Edexcel
Units of data storage: Data capacity is measured in bits and bytes, with 8 bits = 1 byte.OCR
Unpredictable values: Values that are not predictable in advance, produced within a chosen range and useful for games, simulations, sampling and testing.OCR
Unsigned 8-bit range 0 to 255: The range of values represented by 8-bit patterns interpreted as unsigned, running from 0 to 255.Pearson Edexcel
Unsigned integer representation: Every bit is used for magnitude, so an 8-bit unsigned pattern ranges from 00000000 (0) to 11111111 (255).Pearson Edexcel
Unsigned range 0 to 2ⁿ − 1: With n bits there are 2ⁿ possible bit patterns, and for unsigned values these give the range 0 to 2ⁿ − 1.Pearson Edexcel
User interface: The part of the system that lets a person interact with the computer, commonly through a graphical user interface or command line.OCR
User management: Creates and controls user accounts, sets passwords and permissions, and keeps different users' settings and files separate.Pearson Edexcel
Using test data: Running the program, comparing actual output with expected output, and recording the outcome.OCR
Utility software: Small, focused tools that keep a computer usable once the operating system is installed, each solving one housekeeping problem.OCR

V

Variable: A named store whose value can change during execution.Pearson Edexcel
Variable values at a given point: The value read from the row at the specified point in a trace table, rather than from the final row.Pearson Edexcel
variables and constants: A program stores changing data in variables and fixed values in constants, each with a meaningful identifier and an appropriate data type.OCR
Virtual memory: A technique that lets a computer run programs larger than the available physical RAM by using secondary storage as an overflow area.OCR
Virus: Attaches to a legitimate file and spreads when that file is run.Pearson Edexcel
Volatile memory: Memory whose contents are lost when the power is removed, as is the case with RAM.OCR
Volatility: The property by which RAM loses its contents when power is removed, whereas ROM keeps its contents when power is removed.OCR
Volatility and data persistence: RAM is volatile and loses its contents when power is removed, so secondary storage is needed to provide non-volatile storage for data that must persist.OCR
Volatility and persistence: RAM is volatile and loses its contents when power is removed, whereas ROM is non-volatile and keeps firmware permanently.OCR
Von Neumann architecture: Uses a single shared main memory for both program instructions and data, which are fetched and executed in a repeating cycle.OCR
von Neumann stored program concept: Instructions and data are held together in main memory (RAM) as binary.Pearson Edexcel

W

WAN: A network that covers a large geographical area, often connecting LANs across towns, countries or continents, with communication infrastructure usually owned…OCR, Pearson Edexcel
WHERE: Filters rows using a correct comparison operator, enclosing text values in single quotes.OCR
White space: Blank lines and spacing around operators separate logical sections and improve scanning.Pearson Edexcel
Wi-Fi: A family of wireless networking technologies that lets devices join a local area network and exchange data through radio waves instead of cables.OCR
Wired versus wireless: Wired connections such as Ethernet are generally faster and more stable than wireless connections such as Wi-Fi, which can suffer from interference.OCR
Wired versus wireless connectivity: Wired links use a physical cable and usually give higher speed, greater bandwidth and lower latency, while wireless links carry data through the air so…Pearson Edexcel
Wireless standards: Networking that uses radio waves instead of cables, typically following the IEEE 802.11 standards known as Wi-Fi, with devices connecting through a wireless…OCR
Worm: Self-replicates and spreads across networks without needing a host file.Pearson Edexcel
WPA2 or WPA3: Security protocols that encrypt transmissions so that eavesdroppers cannot easily read them.OCR
Write: Sends string data to an opened file, replacing existing content in write mode while append mode adds new data after existing content.OCR

Other terms

1 byte = 8 bits: The conversion keeping bits and bytes distinct, applied when a file size is given in bytes.Pearson Edexcel
1D array: A single list, such as scores[0] to scores[4] holding five test marks.OCR
2D array: A table of rows and columns, such as grid[2][3], where the first index selects the row and the second the column.OCR
8-bit representation: Always write exactly 8 bits when the question asks for 8-bit binary, including leading zeros where necessary.OCR

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