Computer Science: End of Half Term 1 Test - Comp 1

Architecture of CPU, CPU performance, Embedded Systems

Hardware

machines, wiring, physical components of a computer

e.g. mouse, keyboard, circuit board, writing

Software

the programs & other operating info of a computer

e.g. notepad, chrome, files

RAM

• Random Access Memory

• volatile storage - retains no data when turned off

• holds data that is currently being worked on

• very fast as no permanent data is being held

CPU

• Central Processing Unit

• where instructions are processed

• circuits that contain lots of transistors

• works with memory

Computer system

• system that accepts an input, processes it, turns it into an output

• storage is needed to hold input & output

• hardware & software allow this to happen alongside other components

Computer architecture

the design of a computer system and the different components in it

Von Neumann architecture

• modern computers use this architecture

• designed by john von neumann

• common instructions are stored in memory alongside data (stored program concept)

• makes computers more versatile

Stored program concept

• instructions & data are stored as binary digits

• instructions are fetched from memory one at a time in the order they’re sent

• the processer decodes the instruction before executing it

Control unit

• understands instructions

• tells other components what each instruction needs from them

• coordinates all parts and makes sure they’re all working together

ALU

• Arithmetic Logic Unit

• calculator of the CPU

• handles maths & logical operations

Cache

• very fast memory in CPU

• stores frequently used instructions

• reduces need for RAM

Registers

very small, very fast memory location in CPU

MAR, MDR, CIR, PC, ACC

MAR

Memory Address Register - stores memory addresses used when searching for data in RAM

MDR

Memory Data Register - stores data when fetched from MAR

CIR

Current Instruction Register - stores data that is currently being worked on

PC

Program Counter - points to the next instruction to be fetched and increments each time. keeps track of instructions

ACC

Accumulator - stores the result of a calculation

Fetch-execute cycle steps

1. Fetch: next instruction & any data involved is fetched from main memory

2. Decode: instruction is decoded

3. Execute: instruction is carried out

Clock speed

• cycles per second in hertz (Hz)

• the higher the clock speed, the faster it can process instructions

• 1 cycle a sec = 1 Hz = one instruction per sec

Number of cores

• the number of processors linked together on a single chip

• having multiple means that different instructions can be processed simultaneously

• dual core processer = 2 processors linked together ect

Cache size

how big the cache is

Three things that affect CPU performance

clock speed
number of cores
cache size

Clock

• regular electronic pulse that synchronise the stages of the cycle

• basic unit of time in CPU

• each fetch execute cycle takes one clock cycle to complete

Embedded system

• a specialised computer system that completes a specific task

• has all the elements of a typical system

• doesn’t have an operating system because it only does a few tasks

• built into object/device that it controls - a mini computer system inside it

Where are embedded systems held

ROM (permanent memory)

Example of embedded systems

Washing machine

• input is the time, temp, type of wash that the user chooses

• system takes that and runs the machine

• output could be a noise made/display shown to signify that it’s finished

(other examples: microwave, satnav, home security systems)

ROM

• Read Only Memory

• non-volatile - data is retained when power is off

• used for BIOS and bootstrap

BIOS

Basic Input Output System - checks that hardware is working

Bootstrap

the first code that is executed when the computer system is started

Properties of an embedded system

• small

• use less power than general-purpose computer

• lower cost