AQA GCSE Computer Science : Systems Architecture

Hardware

The physical elements of a computer system

Embedded system

A system developed for a single, or set purpose. E.g. A washing machine, microwave, digital watch

General Purpose System

A computer system that can change its purpose by adding more software

Volatile Memory

Memory which is only saved whilst the power is on. E.g. RAM

Non-Volatile Memory

Memory which is saved even when the power is switched off. Eg. ROM

ROM

Non Volatile. Small area of memory which holds the boot up program.

RAM

Volatile memory. Very fast. Holds the currently running programs & files.

Device Driver

A program stored on the hard drive that tells the computer how to communicate with a hardware device such as a printer, mouse, or keyboard.

Scheduler

System software which establishes the order in which instructions are executed by the processor

Address Bus

A physical wire which transmits memory addresses between the CPU and the RAM

Von Neumann architecture

Instructions (programs) and data are stored in the same memory.

Bus

A collection of parallel wires which transmits data between components

Fetch

Fetches the next instruction and data into the CPU from main memory.

Decode

Decodes the instruction so it can carry it out

Execute

Carries out the instruction

CPU

Central Processing Unit. Responsible for all of a computers processing.

Control Unit

Part of the CPU responsible for coordinating and controlling all computer operations

ALU

Arithmetic and Logic Unit. Carries out arithmetic operations (+, -, *, /) and Logic operations - comparing two pieces of data (e.g. is A

System clock

controls the timing of all computer operations - measured in GHz (3 GHz == 3 billion cycles per second)

System performance

CPU performance affected by clock speed, number of cores, cache size

Number of cores

The number of processors linked together on a single chip. Dual core - 2 / Quad core - 4 cores

Cache

Superfast memory in the CPU used to store common instructions / data

Clock speed

Cycles per second - measured in Hertz.

Virtual memory

When RAM is full the operating system uses storage on the hard disk drive as an extension to RAM. Very slow to read / write data.