OCR AS and A Level Computer Science

A collection of vocabulary flashcards covering key terms and concepts from the provided textbook transcript for OCR AS and A Level Computer Science.

Central Processing Unit (CPU)

Also known simply as the processor, it contains components like the control unit, ALU, and dedicated registers to carry out the task of executing instructions.

Control Unit

The part of the CPU that controls and coordinates activities, directing the flow of data between the CPU and other devices, accepting, decoding, and managing instruction execution.

Bus

A set of parallel wires connecting two or more components of a computer, typically consisting of $8$, $16$, $32$, or $64$ lines.

System Bus

The collective name for the data, address, and control buses that connect the processor, memory, and I/O controllers.

Control Bus

A bi-directional bus used to transmit command, timing, and specific status information between system components to ensure access does not lead to conflict.

Data Bus

A bi-directional path, typically consisting of $8$, $16$, $32$, or $64$ separate lines, providing a route for moving data and instructions between system components.

Address Bus

A bus that transmits the memory addresses of words used as operands in program instructions from the processor to memory or I/O controllers.

Word

A fixed size group of digits, typically $16$, $32$, or $64$ bits, which is handled as a unit by the processor.

Arithmetic-Logic Unit (ALU)

The component of the processor that performs arithmetic operations like ADD and SUBTRACT, shift operations, and Boolean logic operations such as AND, OR, NOT, and XOR.

Registers

Special memory cells that operate at very high speed where all arithmetic, logical, or shift operations take place within the CPU.

Program Counter (PC)

A special-purpose register that holds the address of the next instruction to be executed.

Current Instruction Register (CIR)

A register that holds the current instruction being executed, divided into operand and opcode.

Memory Address Register (MAR)

A register that holds the address of the memory location from which data or an instruction is to be fetched or to which data is to be written.

Memory Data Register (MDR)

A register used to temporarily store data read from or written to memory, also known as the memory buffer register.

Fetch-Decode-Execute cycle

The repeated sequence of operations involved in fetching, decoding, and executing a program instruction.

Clock speed

The frequency at which the system clock generates signals to synchronise CPU operations, measured in Gigahertz (GHz), or billions of cycles per second.

Cache

A small amount of expensive, very fast memory inside the CPU that stores instructions fetched from main memory for quick re-access.

Pipelining

A technique that improves efficiency by allowing next instructions to be fetched and buffered while the processor is performing arithmetic or logic operations.

Von Neumann Architecture

A computer architecture specifying shared memory and a bus for both data and instructions, where machine code instructions are fetched and executed serially.

Harvard Architecture

A computer architecture with physically separate memories for instructions and data, often used in embedded Digital Signal Processing (DSP) systems.

CISC (Complex Instruction Set Computers)

An architecture using a large instruction set to accomplish tasks in as few lines of assembly as possible by building complex instructions into hardware.

RISC (Reduced Instruction Set Computers)

An architecture where only simple instructions, each taking one clock cycle, are executed, allowing for techniques like pipelining.

Co-processor

An extra processor used to supplement the functions of the primary processor (CPU), typically for limited functions like floating point arithmetic or graphics.

GPU (Graphics Processing Unit)

A specialised circuit with a massively parallel architecture consisting of thousands of smaller cores designed for handling block visual data simultaneously.

RFID (Radio Frequency Identification)

A technology using microchip transponders and antennae to identify and track items from a distance without line of sight.

Actuator

A motor used in conjunction with sensors to control a mechanism, such as opening a window or starting a pump.

Operating System

A program or set of programs that manages computer operations for the user, acting as a bridge between the user and the hardware.

Paging

A memory management technique where memory is divided into fixed size sections of $4\,KiB$ each.

Segmentation

The logical division of address space into varying length segments based on program structure.

Virtual Memory

A technique using secondary storage as an extension of RAM when physical memory is insufficient to store all currently active jobs.

Interrupt

A signal from software, hardware, or an internal clock to the CPU that causes the processor to suspend execution and call an Interrupt Service Routine (ISR).

Scheduler

The operating system module responsible for allocating processor time to multiple applications effectively.

Distributed Operating System

A parallel processing system that spreads the load of a single job over multiple computer servers.

Utility Software

System software designed to optimise computer performance or perform maintenance tasks like backing up, compressing data, or providing firewalls.

Open Source Software

Software licensed for use without charge, distributed with source code so that anyone can modify or distribute it.

Compiler

A program that translates high-level language source code into hardware-specific machine code (object code) all at once.

Interpreter

A translator that looks at each line of a source program, analyses it for errors, translates it to machine code, and runs it immediately.

Bytecode

An intermediate representation of a language that combines compiling and interpreting, executed by a bytecode interpreter to achieve platform independence.

Waterfall Lifecycle Model

A methodology where software development steps are completed one at a time in a linear sequence from beginning to end.

Agile Modelling

An iterative software development approach where feedback and user participation are used to make incremental changes to prototypes.

Algorithm

A set of clear and precisely stated steps that produce the correct output for any set of valid inputs and always terminate.

Polymorphism

A programming language’s ability to process objects differently depending on their class, often involving overriding inherited methods.

Encapsulation

An object-oriented principle where data (attributes) and methods are wrapped into a single entity, and attributes are often hidden (private) from other classes.

Lossy Compression

Compression that works by removing non-essential information from the original file, resulting in smaller file sizes at the cost of some quality.

Lossless Compression

Compression that records patterns in data rather than actual data, allowing the original file to be reassembled with exact accuracy.

Symmetric Encryption

Also known as private key encryption, it uses the same key to both encrypt and decrypt data.

Asymmetric Encryption

Encryption using two related keys: a public key for encryption and a private key for decryption.

Hashing

A one-way mapping between an arbitrary length input and a usually fixed length output, often used to store passwords securely.

Primary Key

An identifier in a relational database that uniquely identifies a particular record in a table.

Foreign Key

An attribute that creates a join between two tables by being common to both, acting as a primary key in one of them.

Referential Integrity

The measure of ensuring that linked tables in a relational database remain consistent, such as preventing the deletion of a record used elsewhere.

ACID

A set of properties (Atomicity, Consistency, Isolation, Durability) guaranteeing that database transactions are processed reliably.

TCP/IP Protocol Stack

A set of networking protocols (Application, Transport, Network, Link) that work together to pass data packets during network communication.

Packet Switching

A method of communicating data across a network by breaking it into chunks called packets, which may take different routes to their destination.

Firewall

A security checkpoint implemented in hardware or software designed to prevent unauthorised access between two networks.

Big-O Notation

Notation used to express the time complexity or performance of an algorithm relative to the size of the input data set.