1.1 Systems architecture

CPU

The brain of the computer. Carries out instructions. It fetches, decodes and executes instructions from the memory

Memory Address Register (MAR)

Stores the location for data to be fetched from or sent to memory

Memory Data Register (MDR)

Stores data that has been fetched from or is waiting to be sent to memory

Program Counter (PC)

The register that contains the address of the next instruction to be executed

Accumulator (ACC)

Stores the results of any arithmetic or logical operations carried out by the ALU and any inputs

arithmetic/logic unit (ALU)

performs arithmetic operations such as addition

Cache

Small fast memory that stores decoded frequently used instructions. This decreases transfer times and speed up fetch decode execute cycles. This is because the CPU does not need to fetch and decode these instructions.

Fetch-Decode-Execute Cycle

Instructions are fetched from the memory. Decoded in to machine code. Carried out (executed) and then the cycle is repeated

Factors that affect CPU performance

Clock speed, cache size and number of cores

Clock speed

The number of Fetch decode execute cycles carried out per second

Hertz (Hz)

The measurement of the number of cycles per second

Cores

These are processors. Computers may have multiple cores working together. Not all programs are written "sequentially" so having a multiple cores does not always mean that tasks will be exactly as you would expect them to be.

Embedded System

A computer system is part of a bigger device Washing machine dish washer microwave tv MP3 player.

Examples of embedded systems

Washing machine

Dish washer

Microwave

TV

MP3 player.

sound file size

sample rate x duration (s) x bit depth

image file size

colour depth x image height (px) x image width (px)

text file size

bits per character x number of characters

Web Server

A computer connected to the Internet used to store Web page documents and files.

Web client

A computer set up to make requests from a server