computer system internal components - the processor - main memory - i / o controllers - buses...

Computer System Internal components

- The processor- Main memory- I / O controllers- Buses

 External components (peripherals). These include:

- keyboard- mouse- printer - disk drives

Three Box Model (von Neumann architecture)

Processor and MemoryProcessor executes programs and supervises

functioning of the rest of the systemUse Google to find out what Moore’s law is and

put into your notesMemory – use e.g. in Google : define RAM to

find out what it isRAMROMEEPROM

BusesBus: A set of parallel wires

connecting 2 or more components of the computer

System BusesADDRESS BUS – carries address from CPU to

memory

DATA BUS – carries data to CPU from memory

CONTROL BUS – for control signals

These connect the processor, memory and I/O controllers.

Control BusSignals travel in both directionsOnly 1 component can use a bus at a time so

the Control bus transmits command, timing and status information

between componentsto prevent conflict.

Data BusSignals travel in both directions

Typically consists of 6, 16, 32 or 64 separate lines for moving data and instructions between components

The width of the data bus is helps determine overall system performance

Address BusAddresses travel one-way – to memory or to

an I/O controller

The width determines the maximum possible memory capacity of the system

1 line allows 21 maximum addressable cells8 lines allows 28 maximum addressable cells - 256

20 lines allows 220 maximum addressable cells – 1048576

Central Processing Unit

Processor

Main Memoryor

Immediate Access Store

KeyboardInput

Controller

(Disk) I/O Controller

VDU Output Controller

Visual Display Unit

Secondary Store orBacking Store

(e.g. Magnetic Disk)

Keyboard

Control Bus

Data Bus

Address Bus

Components of a simple computer system

Long term storage of programs & data

I/O ControllersThe processor controls and communicates with

a peripheral device through an I/O controller.

Some controllers operate both input & output of bits eg.

Floppy disk controller

Some controllers operate in one direction only eg.

VDU controller - output Keyboard input controller - input

I/O ControllersThe controller is an electronic circuit board

consisting of 3 partsAn interface to connect to the system or I/O

busA set of registersAn interface to connect to the device’s cable