JCE Computer Studies key terms

The main processor chip that fetches, decodes and executes program instructions. It contains the control unit, arithmetic logic unit and registers, and coordinates all other hardware components in a computer system.

The part of the CPU that performs arithmetic operations such as addition and subtraction and logical operations such as AND, OR and comparison. It works on data held in registers under control unit direction.

A very small, very fast storage location inside the CPU used to hold data, addresses or instructions during processing. Registers include the program counter, instruction register and accumulator.

A small, fast memory between the CPU and main memory that stores frequently used instructions and data to reduce average access time. Levels are usually labelled L1, L2 and L3.

Volatile main memory that holds programs and data currently in use. Its contents are lost when power is removed, and it can be read from and written to in any order.

Non-volatile memory whose contents are retained without power and normally cannot be changed by ordinary programs. It typically stores firmware such as the bootstrap loader used at start-up.

The rate, usually in gigahertz, at which the CPU's internal clock issues pulses that pace instruction execution. Higher clock speed can mean faster processing, but architecture also matters.

The repeated sequence of fetching an instruction from memory, decoding it, executing it and storing results. It is also called the fetch-decode-execute cycle and underpins all program execution.

Software stored permanently in read-only or flash memory on a hardware device, such as a router or printer. It controls the device at a low level and can often be updated by the manufacturer.

System software that manages hardware resources, provides services to application programs and offers a user interface. Examples include Windows, Linux, macOS and Android.

A small program that performs housekeeping tasks such as file compression, backup, disk checking, antivirus scanning or formatting. It supports the system rather than doing user productivity work.

Software that lets the operating system communicate with a particular piece of hardware by translating general commands into device-specific instructions. It is often supplied by the hardware manufacturer.

A technique that uses part of secondary storage as an extension of RAM, swapping pages between disk and memory. It lets large programs run on limited memory but is slower than real RAM.

A translator that converts a whole program written in a high-level language into machine code or object code before it is run. Errors are reported after compilation rather than during execution.

A translator that reads, translates and executes a program one statement at a time. It makes debugging easier but generally runs more slowly than compiled code.

A base-2 number system that uses only the digits 0 and 1, each place value being a power of two. Computers use it because electronic circuits have two stable states.

The smallest unit of data in computing, representing a single binary digit, either 0 or 1. Eight bits form a byte, and bits are grouped to represent characters, numbers and instructions.

A group of eight bits treated as one unit of storage. A byte can hold one character in ASCII or a value from 0 to 255 in unsigned form.

A base-16 number system using digits 0-9 and letters A-F. It is a compact shorthand for binary because each hex digit represents exactly four bits.

A method of representing signed integers in binary in which the leftmost bit indicates the sign. It allows subtraction to be carried out as addition and has only one representation of zero.

A character coding scheme that assigns numeric codes to letters, digits, punctuation and control characters. Standard ASCII uses seven bits and covers 128 characters.

A universal character encoding standard that assigns a unique code point to characters in most of the world's writing systems. It supports far more characters than ASCII and is implemented by encodings such as UTF-8.

A set of agreed rules governing how data is formatted, transmitted, received and acknowledged between devices on a network. Common examples are TCP, IP, HTTP and SMTP.

A numeric label assigned to a device on a network so data can be routed to it. IPv4 uses 32 bits and IPv6 uses 128 bits, written in dotted decimal or hexadecimal notation.

A distributed naming service that translates human-readable domain names such as example.com into IP addresses that computers use to locate servers on the internet.

A network device that forwards data packets between different networks, choosing the best path using addressing information. It connects a local network to the internet or links separate subnets.

A network covering a small geographical area such as a school, office or home, in which devices are connected by cables or Wi-Fi. It is usually owned and managed by one organisation.

A network that spans a large geographical area, linking sites across cities or countries, often using telecommunications infrastructure. The internet is the largest example.

A transmission method in which messages are divided into small packets that travel independently and are reassembled at the destination. It uses network links efficiently and is robust to failures.

The address used to locate a resource on the web, typically giving the protocol, domain name and path, for example https://example.com/page. It tells the browser where and how to fetch the resource.

An organised collection of related data stored so that it can be easily accessed, managed and updated. Computerised databases are usually controlled by database management system software.

Software that creates, stores, secures and queries databases, handling tasks such as backup, concurrency control and access rights. Examples include MySQL, Oracle and Microsoft Access.

A field or combination of fields that uniquely identifies each record in a table. It cannot contain duplicate values or nulls and is used to link tables together.

A field in one table that refers to the primary key of another table, creating a relationship between them. It enforces referential integrity by restricting values to those that exist in the referenced table.

A single column in a database table that holds one attribute of the data, such as a surname or price. Each field has a defined data type and applies to every record in the table.

A complete row in a database table, containing one value for each field. A record represents a single entity, such as one student or one order.

A standard language for defining, manipulating and querying relational databases. Statements such as SELECT, INSERT, UPDATE and DELETE operate on tables, and SELECT can filter rows and join tables.