cs definitions paper 1

Arithmetic and Logic Unit (ALU)

• Performs arithmetic calculations

• and logical decisions/comparisons.

Control Unit (CU)

• Decodes instructions

• and sends control signals

• to coordinate the movement of data through the CPU.

Register

• A small, fast,

• temporary storage location

• inside or on the CPU.

Program Counter (PC)

• Holds the address of the

• next instruction to be fetched.

Memory Address Register (MAR)

• Holds the address of the instruction or data

• currently being accessed in memory.

Memory Data Register (MDR)

• Temporarily stores the data or instruction

• that has just been read from,

• or is about to be written to, memory.

Current Instruction Register (CIR)

• Holds the instruction that is

• currently being decoded and executed.

Accumulator (ACC)

• Holds the results of calculations from the ALU

• and stores inputs/outputs from the processor.

Data Bus

• A bi-directional set of wires

• used to transmit data and instructions

• between CPU and memory.

Address Bus

• A uni-directional set of wires used to

• transmit the physical address of the

• memory location to be accessed.

Control Bus

• A bi-directional set of wires used to

• transmit command, timing, and control signals

• from the CU to other components.

Interrupt

• A signal sent to the CPU by a device or software

• requesting immediate attention,

• causing the CPU to temporarily suspend its current execution cycle.

Interrupt Service Routine (ISR)

• A program that runs to

• handle a specific interrupt signal

• before returning control to the original program.

Clock Speed

• The frequency at which the system clock

• generates pulses, measured in Hertz,

• determining the number of F-E cycles per second.

Cache Memory

• Small, fast, quick access memory onboard or near the CPU

• that stores frequently used instructions or data

• to reduce access time.

Pipelining

• A technique where one instruction can be fetched

• while another is being decoded and another is executed.

Von Neumann Architecture

• An architecture where data and instructions

• share a common memory space

• and share a single bus.

Harvard Architecture

• An architecture where data and instructions

• are stored in physically separate memory units

• with dedicated, independent buses.

CISC (Complex Instruction Set Computer)

• A processor design with a large instruction set

• where complex instructions take multiple clock cycles

• and vary in length.

RISC (Reduced Instruction Set Computer)

• A processor design with a small, optimised instruction set

• where each simple instruction takes one clock cycle.

GPU (Graphics Processing Unit)

• A specialised electronic circuit

• designed with thousands of small cores

• optimised for handling parallel processing tasks.

Co-processor

• A secondary, specialised processor

• used to supplement the functions of the

• primary processor by performing specific tasks.

Optical Storage

• Media where data is read and written

• using lasers to track changes in reflectivity (pits and lands).

Magnetic Storage

• Media that stores data by

• magnetising microscopic iron particles on a disk

• into north or south polarities

• to represent binary states.

Solid State Storage

• Non-volatile storage with no moving parts

• that uses electronic circuits and flash memory

• to trap electrons and store data.

RAM (Random Access Memory)

• Volatile main memory that can be

• read from and written to,

• storing programs and data currently in use.

ROM (Read Only Memory)

• Non-volatile memory that

• cannot be written to,

• storing bootstrap loaders and BIOS instructions.

Virtual Memory

• A section of secondary storage

• allocated to act as temporary RAM

• when physical volatile memory is full.

Paging

• Memory is divided into fixed-size physical blocks

• called pages,

• which are mapped to logical memory

• without needing to be contiguous.

Segmentation

• Memory is divided into variable-size logical blocks

• called segments

• based on the logical structure of the program.

Virtual Machine

• A software-based emulation of a complete computer system

• that runs an operating system

• and applications as if it were physical hardware.

BIOS (Basic Input/Output System)

• The initial firmware program executed

• when a computer powers up

• to initialise hardware, perform a POST check, and load the operating system.

Device Driver

• A program that acts as a translator,

• allowing the OS to communicate

• directly with a specific hardware peripheral.

Operating System (OS)

• Core system software that

• Memory management

• User interface (provides it)

• Multitasking

• Platform to run software

• Security

• Scheduling

• Interrupts

Utility Software

• System programs designed to perform

• specific maintenance, configuration, or housekeeping tasks.

Open Source Software

• Software where the source code is freely available

• to the public to view, modify, and redistribute/amend

Proprietary Software

• Closed-source software owned by an individual or company

• where the user buys a license

• but cannot access or modify the source code.

(source code is not available to the public)

Compiler

• A translator that converts the entire source code

• written in a high-level language into machine code

• all at once, producing an independent executable file.

Interpreter

• A translator that converts and executes

• high-level source code line-by-line,

• stopping and reporting immediately if an error is found.

Assembler

• A translator that converts

• low-level assembly language mnemonics

• directly into binary machine code.

Bytecode

• An intermediate, platform-independent code

• produced by a compiler

• designed to be executed by a virtual machine.

Waterfall Lifecycle

• A sequential development model

• where each phase must be completed and documented

• before the next phase begins.

Agile Methodologies

• An iterative development approach

• focused on flexibility, continuous user feedback,

• and producing frequent, working software increments.

Extreme Programming (XP)

• An agile software development framework that

• emphasises code quality

• through pair programming, testing, and continuous rapid releases.

RAD (Rapid Application Development)

• A methodology that prioritises

• prototyping and fast, iterative user feedback

• over long-term structural planning.

Integer

• A data type representing

• a whole number with

• no fractional or decimal part.

Real / Float (OCR Def)

A data type representing a number containing a fractional or decimal part.

Character (OCR Def)

A data type representing a single text symbol, letter, digit, or punctuation mark.

String (OCR Def)

A data type representing a sequence of zero or more characters.

Boolean (OCR Def)

A data type that can only store one of two logical values: True or False.

Array (OCR Def)

A static, indexable, contiguous data structure that stores a fixed number of elements of the same data type.

Linked List (OCR Def)

A dynamic data structure where each element (node) contains a data field and a pointer containing the address of the next node.

Stack (OCR Def)

A Last-In, First-Out (LIFO) dynamic data structure where elements are added (pushed) and removed (popped) from the top.

Queue (OCR Def)

A First-In, First-Out (FIFO) dynamic data structure where elements are added (enqueued) at the back and removed (dequeued) from the front.

Hash Table (OCR Def)

A data structure that stores key-value pairs, using a hashing algorithm to compute an index indicating where the data is stored.

Immediate Addressing (OCR Def)

The operand field contains the actual data value to be used in the instruction.

Direct Addressing (OCR Def)

The operand field contains the memory address where the data value is stored.

Indirect Addressing

The operand field contains a memory address that points to another memory location holding the data.

Indexed Addressing (OCR Def)

The operand address is added to the contents of the Index Register to determine the final target memory location.

Protocol (OCR Def)

A set of rules that govern and standardise data transmission and communication across a network.

Packet Switching (OCR Def)

A data transmission method where messages are broken down into packets, sent independently across different routes, and reassembled at the destination.

Client-Side Processing (OCR Def)

Scripts that are executed directly on the user's local web browser without sending data back to the server.

Server-Side Processing (OCR Def)

Scripts executed on the web server to process requests, query databases, or handle authentication before sending an HTML page back.

Primary Key (OCR Def)

A unique identifier for a specific record within a relational database table.

Foreign Key (OCR Def)

An attribute in a database table that links to a primary key in another table to establish a relationship.

SQL (Structured Query Language) (OCR Def)

A declarative programming language used to manage, query, and manipulate data within a relational database.

Atomicity (ACID) (OCR Def)

A database property ensuring a transaction is completely processed or not processed at all; it cannot be partially completed.

Consistency (ACID) (OCR Def)

A database property ensuring a transaction only transitions the database from one valid state to another, maintaining all validation rules.

Isolation (ACID) (OCR Def)

A database property ensuring the concurrent execution of multiple transactions leaves the database in the same state as if they ran sequentially.

Durability (ACID) (OCR Def)

A database property ensuring that once a transaction is committed, its changes remain saved even in the event of a system crash or power cut.

Class (OCR Def)

A blueprint or template that defines the attributes (data) and methods (behaviours) for creating objects.

Object (OCR Def)

A concrete instance of a class that holds actual data values.

Instantiation (OCR Def)

The process of allocating memory and creating a physical object from a class blueprint.

Encapsulation (OCR Def)

Gathering attributes and methods together into a single structure (class) while restricting direct access using private modifiers.

Inheritance (OCR Def)

The mechanism by which a subclass inherits the attributes and methods of a parent superclass.

Polymorphism (OCR Def)

The property that allows different objects to interpret the same method call or message in unique ways.

Data Protection Act 2018 / GDPR (OCR Def)

Legislation governing how personal data can be legally collected, processed, and stored by organisations.

Computer Misuse Act 1990 (OCR Def)

Legislation making unauthorised access to computer material (hacking) and modifying files without permission illegal.

Copyright, Designs and Patents Act 1988 (OCR Def)

Legislation making it illegal to copy, distribute, or pirate intellectual property without the owner's explicit permission.

Regulation of Investigatory Powers Act 2000 / RIPA (OCR Def)

Legislation regulating the powers of public bodies to carry out surveillance, intercept digital communications, and demand decryption keys.