IGCSE Computer Science Cheat Sheet

Binary (Base 2)

A number system that uses two digits, 0 and 1.

Decimal (Base 10)

A number system that uses ten digits, 0-9.

Hexadecimal (Base 16)

A number system that uses sixteen digits, 0-9 and A-F.

ASCII

A 7-bit character encoding scheme that supports 128 characters.

Unicode

A character encoding standard that supports all languages, using 16 bits or more.

Sample Rate

The number of samples taken per second in sound representation, measured in Hz.

Bit Depth

The number of bits used for each sample in sound representation; higher depth means better quality.

Bit Rate

The product of sample rate, bit depth, and number of channels.

Resolution

The number of pixels in an image, typically described by width x height.

Colour Depth

The number of bits used to represent the color of a single pixel.

Lossy Compression

A type of compression that reduces file size by removing some data and quality.

Lossless Compression

A type of compression that allows original data to be perfectly reconstructed with no loss.

Serial Transmission

Transmission method where bits are sent one at a time over a single wire.

Parallel Transmission

Transmission method where multiple bits are sent simultaneously using multiple wires.

Simplex Transmission

Data transmission method where data flows in one direction only.

Half-Duplex Transmission

Data transmission method where data flows in both directions, but only one at a time.

Full-Duplex Transmission

Data transmission method where data flows in both directions simultaneously.

Parity Bit

An extra bit added to data to ensure that the total number of 1s is even or odd.

Checksum

A calculated value sent with data that is used to check for errors.

ARQ (Automatic Repeat reQuest)

A method that requests retransmission of data if errors are detected.

Symmetric Encryption

A type of encryption where the same key is used for both encryption and decryption.

Asymmetric Encryption

A type of encryption that uses a public key for encryption and a private key for decryption.

ALU (Arithmetic Logic Unit)

The component of a CPU that performs arithmetic and logic operations.

Control Unit (CU)

The part of the CPU that directs data flow and manages instruction execution.

Registers

Small, fast storage locations within the CPU used to hold temporary data.

Program Counter (PC)

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

Memory Address Register (MAR)

A register that holds the address of the data/instruction to be fetched from memory.

Memory Data Register (MDR)

A register that temporarily holds data being transferred to or from memory.

Current Instruction Register (CIR)

A register that holds the instruction currently being executed by the CPU.

Accumulator

A register that stores intermediate results from operations performed by the ALU.

Address Bus

A communication pathway that carries memory addresses from the CPU.

Data Bus

A communication pathway that transfers actual data between components.

Control Bus

A pathway used to send control signals from the CPU to other components.

Fetch-Decode-Execute Cycle

The process by which a CPU fetches an instruction, decodes it, and executes it.

Clock Speed

The speed at which a CPU executes instructions, measured in hertz.

Cache Size

The amount of fast memory available to a CPU for storing frequently used data.

Number of Cores

The amount of independent processing units within a CPU, affecting parallel processing.

Embedded Systems

Dedicated systems designed to perform specific functions within larger devices.

AND Gate

A logic gate that outputs true only if all inputs are true.

OR Gate

A logic gate that outputs true if at least one input is true.

NOT Gate

A logic gate that inverts its input.