GCSE-Computer-Science-Theory

Notes for the AQA GCSE Computer Science (4512/1) theory examination Content based on BourneToCode

The CPU

Basics

A CPU is an integrated circuit that is responsible for performing arithmetic, logical and I/O operations.
CPUs perform these operations as instructed by a computer program.
A CPU is generally made up of two components
An arithmetic logic unit (ALU)
A control unit (CU)

A CPU works in 4 basic stages:

Fetch - Instructions are fetched from the program in memory.

Decode - Instructions are broken up for assignment to parts of the CPU

Execute - Calculations and Logical operations are performed (such as addition)

Writeback - Results of calculations are written back to memory.

Exam Definitions

Computer System

Definition: Hardware and software working together to create a working solution

PSU

Definition: Power supply to convert main AC to DC voltage for the computer

Motherboard

Definition: The circuit-board to which all other core components are connected

CPU

Definition: A chip responsible for performing calculations These perform instructions at a particular clock-frequency (measured in GHz) which determines how fast they can process data.
Multi-core machines can perform tasks simultaneously where this is desired.