Reference

Computer Science Glossary

203 terms from the Cambridge O Level 2210 / IGCSE 0478 and AS & A Level 9618 syllabuses, defined in the words that earn the mark. Each one links to the topic where it is taught — and the flashcards drill 1,600 more.

A* algorithmA2 Level: Graph search that chooses the node with the lowest g + h (cost so far + heuristic estimate to the goal).; Artificial Intelligence · A2 Level
Abstract data type (ADT)All levels: A data type defined by its data and operations, independent of how it is implemented, e.g. stack, queue, linked list.; Algorithm Design and Problem-Solving · O Level / IGCSE Algorithm Design and Problem-Solving · AS Level
AbstractionAll levels: Removing unnecessary detail to focus on what matters for solving the problem.; Algorithm Design and Problem-Solving · O Level / IGCSE Algorithm Design and Problem-Solving · AS Level
Accumulator (ACC)All levels: Register that holds the result of calculations carried out by the ALU.; Hardware · O Level / IGCSE
ActuatorAll levels: An output device that produces physical movement, e.g. a motor, valve or pump.; Automated and Emerging Technologies · O Level / IGCSE Hardware · AS Level
Addressing modeAS Level: The way the operand of an instruction is interpreted: immediate, direct, indirect, indexed or relative.; Processor Fundamentals · AS Level
AlgorithmAll levels: An ordered set of unambiguous steps that solves a problem or performs a task.; Algorithm Design and Problem-Solving · O Level / IGCSE Algorithm Design and Problem-Solving · AS Level
ArrayAll levels: A data structure holding a fixed number of items of the same data type under one identifier, accessed by index.; Programming · O Level / IGCSE Data Types and Structures · AS Level
Artificial intelligenceAll levels: A branch of computer science dealing with systems that simulate intelligent behaviour: collecting data, applying rules, reasoning and learning.; Automated and Emerging Technologies · O Level / IGCSE Artificial Intelligence · A2 Level
Artificial neural networkA2 Level: Layers of connected nodes with weighted connections that are adjusted during training (e.g. by back-propagation).; Automated and Emerging Technologies · O Level / IGCSE Artificial Intelligence · A2 Level
ASCIIAll levels: A character set that gives each character a 7-bit (extended: 8-bit) binary code, e.g. 'A' = 65.; Data Representation · O Level / IGCSE
AssemblerAll levels: Translator that converts assembly-language mnemonics into machine code.; Software · O Level / IGCSE System Software · AS Level
Asymmetric encryptionAll levels: Encryption using a key pair: a public key to encrypt and a matching private key to decrypt.; Security · A2 Level
Automatic Repeat reQuest (ARQ)O Level / IGCSE: Error-control method using acknowledgements and timeouts: data is re-sent if no positive acknowledgement arrives in time.
Backus-Naur FormA2 Level: A formal notation for describing the syntax of a language using production rules.
Base caseA2 Level: The condition in a recursive subroutine that stops the recursion without a further call.; Automated and Emerging Technologies · O Level / IGCSE Databases · O Level / IGCSE Databases · AS Level
Big O notationA2 Level: Describes how an algorithm's time or space grows with input size (O(1), O(log n), O(n), O(n²)).; Computational Thinking and Problem-Solving · A2 Level
BinaryAll levels: Base-2 number system using only the digits 0 and 1; each place value is a power of 2.; Data Representation · O Level / IGCSE Computational Thinking and Problem-Solving · A2 Level
Binary searchA2 Level: Repeatedly comparing the target with the middle item of a sorted list and discarding the half that cannot contain it.; Data Representation · O Level / IGCSE Computational Thinking and Problem-Solving · A2 Level
Binary treeA2 Level: A data structure in which each node has at most two children (left and right pointers).; Data Representation · O Level / IGCSE Computational Thinking and Problem-Solving · A2 Level
Binary-coded decimal (BCD)AS Level: Each denary digit stored separately as a 4-bit binary number.
Bit depthAS Level: The number of bits used to store each sample or pixel.; Information Representation · AS Level Communication · AS Level Communication and Internet Technologies · A2 Level
Bit maskAS Level: A binary pattern used with AND, OR or XOR to test, set or clear particular bits.; Information Representation · AS Level Communication · AS Level Communication and Internet Technologies · A2 Level
BitmapAS Level: An image stored as a grid of pixels, each with a binary colour value.; Information Representation · AS Level
BlockchainO Level / IGCSE: A shared, distributed digital ledger of time-stamped transactions in which each block holds the hash of the previous block.; The Internet and Its Uses · O Level / IGCSE
Brute-force attackAll levels: Trying every possible password or key combination until the correct one is found.
Bubble sortAll levels: Sorting by repeatedly comparing adjacent items and swapping them if they are in the wrong order.; Algorithm Design and Problem-Solving · O Level / IGCSE
BufferAS Level: A temporary area of memory that holds data being transferred between devices working at different speeds.; Hardware · AS Level
BYREFAS Level: Parameter passed by reference — the procedure works on the caller's actual variable.; Programming · AS Level
BYVALAS Level: Parameter passed by value — the procedure works on a copy.; Programming · AS Level
CacheAll levels: Small, fast memory close to the CPU that stores frequently used instructions and data.; Hardware · O Level / IGCSE
Check digitAll levels: An extra digit calculated from the other digits and added to a number (e.g. ISBN) so input errors can be detected.; Data Transmission · O Level / IGCSE Security, Privacy and Data Integrity · AS Level
ChecksumAll levels: A value calculated from a block of data and sent with it; the receiver recalculates to detect errors.; Data Transmission · O Level / IGCSE Security, Privacy and Data Integrity · AS Level
Circuit switchingA2 Level: A dedicated path is set up between sender and receiver for the whole communication.; Boolean Logic · O Level / IGCSE Communication and Internet Technologies · A2 Level
ClassA2 Level: A blueprint defining the attributes and methods of objects.; Further Programming · A2 Level
Client–server modelAS Level: Network model in which clients request services and resources from central servers.
Clock speedAll levels: The number of fetch–execute cycles the CPU can perform per second, measured in Hz.
Cloud storageO Level / IGCSE: Storing data on remote servers accessed over the internet, maintained by a third party.; Communication · AS Level
Code optimisationA2 Level: Compilation stage that makes the object code faster or smaller without changing what it does.; Data Representation · O Level / IGCSE Hardware · O Level / IGCSE Algorithm Design and Problem-Solving · O Level / IGCSE
Colour depthAll levels: The number of bits used to represent the colour of each pixel.; Data Representation · O Level / IGCSE Information Representation · AS Level
CompilerAll levels: Translates the whole high-level program into machine code before it runs; produces an executable and a list of all errors.; Software · O Level / IGCSE System Software · AS Level
ConstantAll levels: A named value that cannot change while the program runs.; Programming · O Level / IGCSE Programming · AS Level
CookieO Level / IGCSE: A small text file stored by the browser for a website, holding data such as log-in state or preferences.; The Internet and Its Uses · O Level / IGCSE
CopyrightAS Level: The legal right of creators to control copying, distribution and adaptation of their original work, including software.; Ethics and Ownership · AS Level
CoreAll levels: An independent processing unit in a CPU; more cores can process more instructions at the same time.
Corrective / adaptive / perfective maintenanceAS Level: Fixing bugs / changing the program for new requirements or environments / improving performance or usability.
Data dictionaryAS Level: Metadata about a database: tables, fields, data types, keys, validation rules.; Data Representation · O Level / IGCSE Data Transmission · O Level / IGCSE Algorithm Design and Problem-Solving · O Level / IGCSE
Data integrityAS Level: The accuracy, completeness and consistency of data.; Data Representation · O Level / IGCSE Data Transmission · O Level / IGCSE Algorithm Design and Problem-Solving · O Level / IGCSE
Data privacyAS Level: The right of individuals to keep their personal data confidential and control how it is used.; Data Representation · O Level / IGCSE Data Transmission · O Level / IGCSE Algorithm Design and Problem-Solving · O Level / IGCSE
DBMSAS Level: Database management system: software that manages a database, with a data dictionary, query processor, security and backup.
DDL / DMLAS Level: Data definition language creates/changes the structure (CREATE, ALTER); data manipulation language queries/changes data (SELECT, INSERT, UPDATE, DELETE).; Databases · AS Level
DDoS attackAll levels: Distributed denial of service: many compromised computers flood a server with requests so genuine users cannot access it.; The Internet and Its Uses · O Level / IGCSE
De Morgan's lawsA2 Level: NOT(A AND B) = NOT A OR NOT B; NOT(A OR B) = NOT A AND NOT B — 'break the bar, change the sign' (9618 §15.2).; Data Representation · O Level / IGCSE Hardware · O Level / IGCSE Software · O Level / IGCSE
Declarative programmingA2 Level: Writing facts and rules; the language finds solutions that satisfy a goal (e.g. Prolog).; Further Programming · A2 Level
DecompositionAll levels: Breaking a problem down into smaller sub-problems that are easier to solve.; Algorithm Design and Problem-Solving · O Level / IGCSE Algorithm Design and Problem-Solving · AS Level
Deep learningA2 Level: Machine learning using artificial neural networks with many hidden layers.
Digital certificateA2 Level: An electronic document from a Certificate Authority binding a public key to an identity.; Security · A2 Level
Digital currencyO Level / IGCSE: Money that exists only in electronic form, e.g. cryptocurrency tracked by a blockchain.; Security · A2 Level
Dijkstra's algorithmA2 Level: Finds the shortest path from a source node to all other nodes in a weighted graph.
Disk thrashingA2 Level: The computer spends more time swapping pages between RAM and disk than executing instructions.
DNSAll levels: Domain name system: servers that translate domain names into IP addresses.; The Internet and Its Uses · O Level / IGCSE Communication · AS Level
DRAMAS Level: Dynamic RAM: uses capacitors that must be refreshed, cheaper and denser — used for main memory.; Hardware · AS Level
Dry runAll levels: Working through an algorithm by hand with test data, usually recording values in a trace table.
Echo checkO Level / IGCSE: The receiver sends the data back to the sender, which compares it with the original to detect transmission errors.
EEPROMAS Level: ROM that can be erased and rewritten electrically while in the circuit.; Hardware · AS Level
Embedded systemO Level / IGCSE: A computer system with a dedicated function built into a larger device (e.g. a washing machine).; Hardware · O Level / IGCSE Hardware · AS Level
EncapsulationA2 Level: Keeping an object's attributes private and accessing them only through its methods.; Further Programming · A2 Level
EncryptionAll levels: Scrambling data with a key so that it is meaningless if intercepted.; Data Transmission · O Level / IGCSE Security · A2 Level
Entity-relationship (E-R) diagramAS Level: A diagram showing entities and the relationships (1:1, 1:M, M:M) between them.
Exception handlingA2 Level: Code that detects a run-time error and responds to it without the program crashing (TRY … EXCEPT).; Further Programming · A2 Level
Expert systemO Level / IGCSE: AI that mimics a human expert using a knowledge base, rule base, inference engine and user interface.; Automated and Emerging Technologies · O Level / IGCSE
Fetch–decode–execute cycleAll levels: The repeated process by which the CPU fetches an instruction from memory, decodes it and carries it out.; Hardware · O Level / IGCSE
FirewallAll levels: Monitors and filters network traffic between a computer/network and the internet according to rules.; The Internet and Its Uses · O Level / IGCSE
FirmwareAll levels: Software stored in non-volatile memory (ROM/flash) that controls a device's hardware, e.g. the bootstrap loader.; Software · O Level / IGCSE
Flip-flopA2 Level: A logic circuit with two stable states that stores one bit; SR and JK types are the building blocks of registers and SRAM (9618 §15.2).; Hardware and Virtual Machines · A2 Level
FlowchartAll levels: A diagram using standard symbols joined by flow lines to show the steps of an algorithm.; Algorithm Design and Problem-Solving · O Level / IGCSE Algorithm Design and Problem-Solving · AS Level
Foreign keyAS Level: A field in one table that is the primary key of another table, used to link the tables.; Databases · AS Level
Full adderA2 Level: A logic circuit that adds two bits plus a carry-in, producing a sum and a carry-out; built from two half adders and an OR gate.; Hardware and Virtual Machines · A2 Level
FunctionAll levels: A named subroutine that returns a single value to the point where it was called.; Programming · O Level / IGCSE Programming · AS Level
Global variableAll levels: A variable declared outside all subroutines that can be used anywhere in the program.
Hashing algorithm (files)A2 Level: A calculation on a record's key that gives the address where the record is stored in a random-access file.; Data Representation · A2 Level Security · A2 Level
HexadecimalAll levels: Base-16 number system (0–9, A–F); one hex digit represents 4 bits, so it is a compact way to write binary.; Data Representation · O Level / IGCSE
High-level languageAll levels: A programming language close to English, portable between machines, where one statement becomes many machine instructions.
HTTPSAll levels: The secure version of HTTP, using SSL/TLS to encrypt data between browser and web server.; The Internet and Its Uses · O Level / IGCSE
IDEAll levels: Integrated development environment: software for writing programs, with an editor, run-time environment, translator, error diagnostics and auto-completion.; Software · O Level / IGCSE System Software · AS Level Algorithm Design and Problem-Solving · AS Level
Identifier tableAS Level: A table listing each identifier in an algorithm with its data type and description.; Algorithm Design and Problem-Solving · AS Level
Image resolutionAll levels: The number of pixels in an image, given as width × height.
InheritanceA2 Level: A subclass gains the attributes and methods of its superclass and can add or override them.; Further Programming · A2 Level
Insertion sortA2 Level: Builds a sorted list one item at a time by inserting each item into its correct place among those already sorted.
Instruction setAll levels: The complete list of machine-code instructions that a particular CPU can decode and execute.
InterpreterAll levels: Translates and executes a high-level program one line at a time; stops at the first error.; Software · O Level / IGCSE System Software · AS Level
InterruptAll levels: A signal to the processor that an event needs immediate attention; the current task is paused and an ISR runs.; Software · O Level / IGCSE Processor Fundamentals · AS Level
IP addressAll levels: A logical address given to a device on a network so data can be routed to it; IPv4 is 32-bit, IPv6 is 128-bit.; Hardware · O Level / IGCSE Communication · AS Level Ethics and Ownership · AS Level
IterationAll levels: Repeating a set of statements: count-controlled (FOR), pre-condition (WHILE) or post-condition (REPEAT) loops.; Algorithm Design and Problem-Solving · AS Level
Karnaugh mapA2 Level: A grid method for simplifying Boolean expressions by grouping adjacent 1s (9618 §15.2).; Hardware and Virtual Machines · A2 Level
KernelAS Level: The core of the operating system that manages memory, processes and hardware.
LAN / WANAS Level: Local area network on one site / wide area network over a large geographical area.; Communication · AS Level
Lexical analysisA2 Level: First stage of compilation: removes white space and comments and converts the source into tokens.; System Software · A2 Level
Library programAS Level: Pre-written, pre-tested code that can be linked into a program, e.g. a DLL.; Programming · AS Level
Linear searchAll levels: Checking each item of a list in turn until the target is found or the list ends.; Algorithm Design and Problem-Solving · O Level / IGCSE
Linked listAll levels: A dynamic data structure in which each node holds data and a pointer to the next node.
Local variableAll levels: A variable declared inside a subroutine; it exists only while that subroutine runs.
Logic gateAll levels: An electronic component that performs a Boolean operation (NOT, AND, OR, NAND, NOR, XOR) on binary inputs.; Boolean Logic · O Level / IGCSE Hardware · AS Level Processor Fundamentals · AS Level
Logical shiftAll levels: Moving every bit in a register left or right; vacated positions are filled with 0 and bits shifted out are lost.; Processor Fundamentals · AS Level
Lossless compressionAll levels: Reduces file size without losing any data, so the original can be restored exactly (e.g. run-length encoding).
Lossy compressionAll levels: Reduces file size by permanently removing data the user is unlikely to notice (e.g. JPEG, MP3).
Low-level languageAll levels: Machine code or assembly language; specific to one type of CPU and gives direct control of the hardware.
MAC addressAll levels: A unique 48-bit physical address given to a network interface card by the manufacturer, written in hexadecimal.; Hardware · O Level / IGCSE Automated and Emerging Technologies · O Level / IGCSE Hardware and Virtual Machines · A2 Level
Machine learningAll levels: A type of AI in which a program can adapt its own processes or data from experience, improving without being explicitly reprogrammed.; Automated and Emerging Technologies · O Level / IGCSE Hardware and Virtual Machines · A2 Level
MalwareAll levels: Malicious software, e.g. viruses, worms, Trojan horses, spyware, adware and ransomware.; The Internet and Its Uses · O Level / IGCSE Security, Privacy and Data Integrity · AS Level
Mantissa & exponentA2 Level: The two parts of a floating-point number: significant digits (mantissa) and the power of two scale (exponent).; Data Representation · A2 Level
Massively parallel computerA2 Level: A computer with a very large number of processors working together on parts of the same problem.; Hardware and Virtual Machines · A2 Level
Memory address register (MAR)All levels: Register holding the address of the memory location currently being read from or written to.; Hardware · O Level / IGCSE System Software · A2 Level
Memory data register (MDR)All levels: Register holding the data or instruction just read from, or about to be written to, memory.; Hardware · O Level / IGCSE System Software · A2 Level
Mesh topologyAS Level: Devices connect to several others, so there are many routes between any two nodes.
Network interface card (NIC)O Level / IGCSE: Hardware that lets a device connect to a network; it holds the device's MAC address.; Artificial Intelligence · A2 Level
Normal / abnormal / extreme / boundary dataAll levels: Test data that should be accepted / rejected / is at the limit of the accepted range / is at and just beyond the limit.; Databases · AS Level Data Representation · A2 Level
Normalisation (databases)AS Level: Organising tables to remove redundancy and update anomalies (1NF, 2NF, 3NF).; Databases · AS Level Data Representation · A2 Level
ObjectA2 Level: An instance of a class.; Further Programming · A2 Level
Open sourceAS Level: Software whose source code is available to users to study, modify and redistribute under its licence.; Ethics and Ownership · AS Level Data Types and Structures · AS Level
Operating systemAll levels: System software that manages hardware, memory, files, processes, security and the user interface.; Software · O Level / IGCSE System Software · AS Level
OverflowAll levels: When a calculation produces a result too large to be stored in the available number of bits.; Data Representation · O Level / IGCSE Data Representation · A2 Level
PacketAll levels: A small unit of data sent over a network, made of a header (destination/source IP, packet number), payload and trailer.; Data Transmission · O Level / IGCSE
Packet switchingAll levels: Data split into packets that may take different routes and are reassembled at the destination.; Data Transmission · O Level / IGCSE
PagingA2 Level: Memory management that divides memory into fixed-size frames and processes into pages of the same size.; System Software · A2 Level
Parallel transmissionO Level / IGCSE: Several bits sent at the same time down several wires.; Hardware and Virtual Machines · A2 Level
ParameterAll levels: A value passed into a subroutine when it is called.; Programming · O Level / IGCSE
ParityAll levels: An extra bit added so the number of 1s is even (or odd), used to detect single-bit errors.; Data Transmission · O Level / IGCSE Security, Privacy and Data Integrity · AS Level
Peer-to-peerAS Level: Network model in which every computer has equal status and can share resources directly.; Communication · AS Level
PharmingAll levels: Malicious code or DNS changes that redirect a user from a genuine website to a fake one.; The Internet and Its Uses · O Level / IGCSE Security, Privacy and Data Integrity · AS Level
PhishingAll levels: Fraudulent emails or messages that trick a user into giving personal details, often via a fake website link.; The Internet and Its Uses · O Level / IGCSE Security, Privacy and Data Integrity · AS Level
PipeliningA2 Level: Overlapping the fetch, decode and execute stages of successive instructions to increase throughput.; Hardware and Virtual Machines · A2 Level
PolymorphismA2 Level: Objects of different classes responding to the same method call in class-specific ways.; Further Programming · A2 Level
Primary keyAll levels: A field (or fields) whose value uniquely identifies each record in a table.; Databases · O Level / IGCSE Databases · AS Level
ProcedureAll levels: A named subroutine that performs a task and does not return a value.; Programming · O Level / IGCSE Programming · AS Level
Process schedulingA2 Level: The OS deciding which process uses the CPU: e.g. round robin, first come first served, shortest job first.; Automated and Emerging Technologies · O Level / IGCSE Processor Fundamentals · AS Level System Software · A2 Level
Program counter (PC)All levels: Register holding the address of the next instruction to be fetched.; Programming · O Level / IGCSE Programming · AS Level Further Programming · A2 Level
Program development life cycleO Level / IGCSE: The stages of producing a program: analysis, design, coding and testing.; Programming · O Level / IGCSE Programming · AS Level Further Programming · A2 Level
Programming paradigmA2 Level: A style of programming: low-level, imperative (procedural), object-oriented or declarative.; Programming · O Level / IGCSE Programming · AS Level Further Programming · A2 Level
Proxy serverO Level / IGCSE: A server that sits between users and the internet, filtering requests, caching pages and hiding users' IP addresses.; The Internet and Its Uses · O Level / IGCSE
PseudocodeAll levels: A structured, language-independent way of writing an algorithm using programming-like statements.; Algorithm Design and Problem-Solving · O Level / IGCSE Algorithm Design and Problem-Solving · AS Level
Public / private IP addressAS Level: A public IP address is unique on the internet; a private one is used only inside a LAN and reached through NAT.; Data Transmission · O Level / IGCSE Security · A2 Level
Public key infrastructureA2 Level: The system of certificate authorities, digital certificates and key pairs used to verify identities online.; Data Transmission · O Level / IGCSE Security · A2 Level
Quantum cryptographyA2 Level: Using the properties of photons to distribute keys so that any eavesdropping is detected.; Security · A2 Level
QueueAll levels: A first-in first-out (FIFO) data structure with front and rear pointers.
RAMAll levels: Random access memory: volatile primary storage holding the programs and data currently in use.; Hardware · O Level / IGCSE Programming · O Level / IGCSE Hardware · AS Level
RansomwareAll levels: Malware that encrypts a user's files and demands payment for the key.
Rapid application development (RAD)AS Level: A development approach based on quick prototypes and user feedback rather than detailed up-front planning.
RecordAS Level: A composite data type made of fields that can have different data types.; Databases · O Level / IGCSE Data Types and Structures · AS Level
RecursionA2 Level: A function that calls itself, with a base case to stop and a general case that moves towards it.; Computational Thinking and Problem-Solving · A2 Level
Referential integrityAS Level: Every foreign key value must match an existing primary key value in the linked table.; Databases · AS Level
Register Transfer NotationAS Level: Notation describing data movement between registers, e.g. MAR ← [PC].; Processor Fundamentals · AS Level
Reinforcement learningA2 Level: Machine learning where an agent learns by trial and error from rewards and penalties.; Artificial Intelligence · A2 Level
Reverse Polish NotationA2 Level: Postfix notation where operators follow operands; evaluated with a stack without brackets.
RISC / CISCA2 Level: Reduced vs Complex Instruction Set Computer — few simple fixed-length instructions vs many complex ones.; Hardware and Virtual Machines · A2 Level
RobotO Level / IGCSE: A programmable machine with a mechanical structure, electrical components and the ability to be programmed to carry out tasks.; Automated and Emerging Technologies · O Level / IGCSE
ROMAll levels: Read-only memory: non-volatile primary storage holding firmware such as the bootstrap loader.; Hardware · O Level / IGCSE Hardware · AS Level
RouterAll levels: Device that forwards packets between networks using their destination IP addresses.; Hardware · O Level / IGCSE
Run-length encoding (RLE)All levels: Lossless compression that replaces a run of identical values with one copy of the value and a count.; Information Representation · AS Level
Sample rateAll levels: The number of sound samples taken per second, measured in hertz.; Data Representation · O Level / IGCSE
Sample resolutionAll levels: The number of bits used to store each sound sample (bit depth).; Data Representation · O Level / IGCSE
SegmentationA2 Level: Memory management that divides a process into variable-size logical segments.; System Software · A2 Level
SelectionAll levels: Choosing which statements run depending on a condition (IF … THEN … ELSE, CASE).; Algorithm Design and Problem-Solving · AS Level
SensorAll levels: An input device that measures a physical quantity such as temperature, light or pressure.; Automated and Emerging Technologies · O Level / IGCSE Hardware · AS Level
Serial / sequential / random file organisationA2 Level: Records in order of arrival / in key order / at an address calculated from the key.; Data Representation · A2 Level
Serial transmissionO Level / IGCSE: Data sent one bit at a time down a single wire.; Data Representation · A2 Level
SIMD / MIMDA2 Level: Single instruction multiple data / multiple instruction multiple data — parallel processing classifications.; Hardware and Virtual Machines · A2 Level
Simplex / half-duplex / full-duplexO Level / IGCSE: Data in one direction only / both directions but one at a time / both directions at the same time.
Solid-state storageAll levels: Storage with no moving parts that keeps data in NAND flash memory cells by trapping electrons.
SQLAll levels: Structured Query Language: used to define, query and change data in a database.; Databases · O Level / IGCSE
SRAMAS Level: Static RAM: uses flip-flops, needs no refreshing, faster and more expensive — used for cache.; Hardware · AS Level
SSL / TLSA2 Level: Protocols that authenticate a server with its certificate and encrypt data sent between client and server.; The Internet and Its Uses · O Level / IGCSE Security · A2 Level
StackAll levels: A last-in first-out (LIFO) data structure with push and pop operations and a top pointer.; Computational Thinking and Problem-Solving · A2 Level
Stack frameA2 Level: The block on the call stack holding a subroutine call's parameters, local variables and return address.; Computational Thinking and Problem-Solving · A2 Level
Star topologyAS Level: Every device connects to a central switch or hub.
Static / dynamic IP addressAS Level: A static IP address stays the same; a dynamic one is allocated (by DHCP) each time a device connects.
Stepwise refinementAS Level: Breaking each step of an algorithm into smaller steps until each can be written as a program statement.; Algorithm Design and Problem-Solving · AS Level
Structure diagramAll levels: A hierarchical diagram showing how a problem is decomposed into sub-systems.; Algorithm Design and Problem-Solving · AS Level Data Types and Structures · AS Level
Structured EnglishAS Level: A restricted form of English with keywords and indentation used to describe an algorithm.; Algorithm Design and Problem-Solving · AS Level
Stub testingAS Level: Replacing an unfinished module with a simple placeholder so the rest can be tested.; Software Development · AS Level
Supervised / unsupervised learningA2 Level: Machine learning from labelled examples / finding patterns in unlabelled data.; Artificial Intelligence · A2 Level
Symmetric encryptionAll levels: Encryption in which the same secret key is used to encrypt and decrypt.; Security · A2 Level
Syntax analysisA2 Level: Compilation stage that checks the tokens follow the grammar of the language and builds a parse tree.; Software Development · AS Level System Software · A2 Level
TCP/IP stackA2 Level: Four-layer protocol model: application, transport, internet and link.; Communication and Internet Technologies · A2 Level
Trace tableAll levels: A table used to dry-run an algorithm, recording the value of each variable at each step.; Algorithm Design and Problem-Solving · O Level / IGCSE Software Development · AS Level
Truth tableAll levels: A table showing the output of a logic circuit or expression for every combination of inputs.; Boolean Logic · O Level / IGCSE Hardware · AS Level
Two-step verificationAll levels: Authentication that needs a second step (e.g. a code sent to a phone) as well as a password.
Two's complementAll levels: A method of representing signed integers where the MSB has a negative place value.; Data Representation · O Level / IGCSE Information Representation · AS Level
UnicodeAll levels: A character set using up to 32 bits per character so it can represent the characters of all the world's languages and emoji.; Data Representation · O Level / IGCSE
URLO Level / IGCSE: Uniform resource locator: a text address for a web resource, made of protocol, domain name and file path.; The Internet and Its Uses · O Level / IGCSE Communication · AS Level
USBO Level / IGCSE: Universal Serial Bus: a serial interface standard for connecting devices, which also supplies power.; Data Transmission · O Level / IGCSE
User-defined data typeA2 Level: A data type created by the programmer from built-in types, e.g. record, enumerated, pointer, set.
Utility softwareAS Level: System software that helps maintain the computer, e.g. anti-virus, defragmentation, backup, compression.; Software · O Level / IGCSE System Software · AS Level
ValidationAll levels: Automated checks that input data is reasonable (range, type, length, presence, format, check digit).; Algorithm Design and Problem-Solving · O Level / IGCSE Security, Privacy and Data Integrity · AS Level
VariableAll levels: A named memory location whose value can change while the program runs.; Programming · O Level / IGCSE Programming · AS Level
Vector graphicAS Level: An image stored as a list of drawing objects and their properties, so it can be scaled without losing quality.; Information Representation · AS Level
VerificationAll levels: Checking data has been transferred/entered accurately (double entry, visual check).; Algorithm Design and Problem-Solving · O Level / IGCSE Security, Privacy and Data Integrity · AS Level
Virtual machineA2 Level: Software emulation of a computer system, allowing multiple OSs to run on one physical machine.; Hardware · O Level / IGCSE Hardware and Virtual Machines · A2 Level System Software · A2 Level
Virtual memoryAll levels: Part of secondary storage used as if it were RAM when RAM is full; pages are swapped in and out.; Hardware · O Level / IGCSE Hardware and Virtual Machines · A2 Level System Software · A2 Level
Von Neumann architectureAll levels: Computer design in which data and instructions are stored together in the same memory and fetched by the CPU.
Waterfall modelAS Level: A development life cycle in which each stage is completed before the next begins.; Software Development · AS Level
White-box / black-box testingAS Level: Testing with knowledge of the code's paths / testing inputs against expected outputs without looking at the code.; Software Development · AS Level
World Wide WebO Level / IGCSE: The collection of web pages and resources accessed over the internet using a browser and HTTP(S).