BSEH Secondary Computer Science key terms

The smallest unit of digital data, holding exactly one of two values, usually written 0 or 1. Every file, instruction and image is ultimately stored as a sequence of bits.

A group of eight bits treated as one unit. It can represent 256 different values, enough for one character code, and is the usual measure of file and memory size.

A base-2 place value system using only the digits 0 and 1, where each position represents a power of two. Computers use it because hardware circuits have two stable states.

A base-16 system using digits 0-9 and letters A-F. One hexadecimal digit maps exactly to four bits, so it gives a short, readable way to write binary values such as memory addresses and colour codes.

A rule that maps characters to numeric codes so text can be stored as bits. ASCII covers basic English characters, while Unicode covers scripts and symbols from most of the world's writing systems.

The component that fetches, decodes and executes program instructions, performing arithmetic, logic and control operations. Its speed is influenced by clock rate, core count and cache size.

Volatile working memory that holds programs and data currently in use. Its contents are lost when power is removed, and larger capacity allows more applications to run at once.

Non-volatile memory whose contents are written at manufacture or by special equipment and normally only read. It stores firmware such as the startup instructions needed to boot a computer.

A small, very fast memory placed close to the processor that keeps recently or frequently used data and instructions. It reduces the average time the CPU waits for slower main memory.

Non-volatile storage such as hard disks, solid state drives, optical discs or flash drives that keeps data when power is off. It is slower than main memory but far larger and cheaper per unit.

Hardware that moves data between the computer and the outside world. Keyboards, mice and scanners are input devices; monitors, printers and speakers are output devices; touchscreens do both.

Software stored permanently in hardware, usually in ROM or flash memory, that controls a device at a low level. The basic input/output system that starts a computer is a common example.

System software that manages hardware resources, runs programs, controls files and provides a user interface. It schedules processes, allocates memory and enforces access permissions.

The part of an operating system that organises data on storage into files and directories, tracks where each file's blocks are stored, and controls who may read or write them.

The operating system's decision about which ready program gets the processor next and for how long. Common policies include first come first served, shortest job first and round robin.

Translators that convert high-level source code into machine instructions. A compiler translates the whole program before running it; an interpreter translates and executes statements one at a time.

A finite, unambiguous sequence of steps that solves a problem or produces a result for any valid input. Good algorithms are correct, terminate, and use reasonable time and memory.

A diagram using standard symbols such as ovals for start and end, parallelograms for input and output, rectangles for processes and diamonds for decisions, with arrows showing the order of steps.

Structured English-like notation that describes an algorithm's logic without following a particular language's syntax. It lets a programmer plan and check a solution before writing real code.

Repeating a block of statements while a condition holds or for a fixed number of times, using loops such as for and while. Each pass through the loop body is called an iteration.

Choosing between alternative paths in a program using conditions, expressed with if, else-if and else statements or switch constructs. It lets one program behave differently for different inputs.

An expression that evaluates to exactly true or false, built from comparison operators and combined with and, or and not. It typically controls the branch taken by a selection or loop.

A variable is a named storage location whose value can change during execution. Its data type, such as integer, floating point, string or Boolean, fixes what values it may hold and which operations apply.

Changing a value from one data type to another. Implicit conversion happens automatically when it is safe; explicit casting is written by the programmer and may lose information, as when a float becomes an integer.

An indexed collection of elements of the same type stored under one name, accessed by position starting from a fixed index. Traversing an array with a loop is a standard way to process many values.

The position used to select an element of an array or character of a string. In Python and C++ indexing starts at 0, so the first element has index 0 and the last has index length minus one.

Working with sequences of characters: reading them, joining them, finding their length, extracting substrings, comparing them and changing case. Strings are usually immutable, so operations return new strings.

A named block of code that performs a task, optionally takes parameters and optionally returns a value. Functions make programs shorter, easier to test and easier to reuse.

A parameter is the named input declared in a function's definition; an argument is the actual value supplied when the function is called. Arguments are matched to parameters by position or by name.

A technique where a function calls itself on a smaller version of the same problem. Every recursive function needs a base case that stops the calls, otherwise it runs until the stack overflows.

A mistake that breaks the language's grammar rules, such as a missing bracket or misspelled keyword, which prevents the program from compiling or running. It differs from a logic error, which produces wrong output.

The process of finding, diagnosing and fixing errors in a program. It uses reading the code, test data, print statements, breakpoints and step-by-step execution to locate faulty behaviour.

An organised collection of related data stored so it can be searched, updated and shared efficiently. Relational databases store data in tables of rows and columns linked by keys.

A column or combination of columns whose value uniquely identifies each row in a table. It must be unique and never null, and it prevents duplicate records.

A column in one table that holds the primary key value of a row in another table, creating a link between them. It enforces referential integrity so records cannot point to missing rows.

Structured Query Language, used to define, query and modify relational databases. Common statements include SELECT to retrieve rows, INSERT to add them, UPDATE to change them and DELETE to remove them.

A numeric label given to each device on a network so data can be routed to it. IPv4 addresses are 32 bits written as four decimal numbers; IPv6 addresses are 128 bits.

The Domain Name System, a distributed service that translates human-readable domain names into IP addresses. Without it, users would have to remember numeric addresses for every website.

An agreed set of rules for how devices exchange data, covering message format, timing and error handling. Common examples are TCP/IP for internet traffic, HTTP for web pages and SMTP for email.

A Uniform Resource Locator, the address that identifies a resource on the web. It typically includes a scheme such as https, a domain name, an optional path and query parameters.

A social engineering attack that tricks people into revealing passwords or financial details, usually through fake emails, messages or lookalike websites. Checking sender addresses and links helps defend against it.

Software written to harm or gain unauthorised access to a system, including viruses, worms, trojans, spyware and ransomware. Antivirus tools, updates and cautious downloading reduce the risk.

Hardware or software that filters network traffic against rules, allowing approved connections and blocking suspicious ones. It forms a barrier between a private network and the internet.

Converting readable data into an unreadable form using a key, so only someone holding the correct key can recover it. It protects data in transit, as in HTTPS, and data at rest.

A password that is long and mixes character types, avoids names and dictionary words, is unique to one account and is never shared. A password manager helps create and store such passwords.

Creations of the mind, such as software, music, images and writing, protected by law through copyright, patents or trademarks. Using them without permission or licence can be illegal.

A legal agreement stating how a program may be used, copied, modified and distributed. Options range from proprietary licences to open-source licences that permit free use and modification.

Presenting someone else's words, code or ideas as your own without credit. In computing it includes copying code without attribution, and it breaches academic and professional honesty.

The trail of data a person leaves online through posts, searches, comments and browsing. It can persist and be seen by schools, employers and strangers, so it should be managed carefully.

Using digital channels such as messages, social media or games to harass, threaten or humiliate someone repeatedly. It can be reported, blocked and documented with screenshots as evidence.

Computer systems that perform tasks associated with human intelligence, such as recognising images, understanding language or making predictions. Most modern systems learn patterns from large amounts of data.

A branch of artificial intelligence where programs improve at a task by learning patterns from training data rather than being given explicit rules. Quality and bias in that data strongly affect results.

Using remote servers over the internet for storage, processing and software instead of local hardware. It offers flexibility and access from anywhere but depends on connectivity and raises data privacy questions.

A network of everyday physical devices, such as sensors, cameras and appliances, fitted with electronics so they can collect and exchange data online. Weak security on such devices is a common risk.

Inputs chosen to check whether a program behaves correctly, including normal values, boundary values and invalid values. Comparing actual output with expected output reveals logic errors.

Manually tracing a program's statements with sample input, recording each variable's value in a trace table. It helps find logic errors and confirm that loops and conditions behave as intended.