F451 - 3.1.4 Hardware

a. Describe the function and purpose of the control unit, memory unit and ALU (arithmetic logic unit) as individual parts of a computer

CONTROL UNIT

Manages execution of instructions

By sending control signals to other parts of the processor using busses

Controls the fetch/execute cycle

- It decides which instruction to carry out

- Then fetches it, decodes it, and synchronises its execution

Synchronises actions using inbuilt clock

MEMORY UNIT

This is where everything the processor is going to use is stored

Stores the part of the OS currently in use

Stores software currently in use

Stores data needed to carry out those instructions

ARITHMETIC LOGIC UNIT (ALU)

Carries out arithmetic calculations

Carries out logical decisions

Acta as a gateway to the processor

b. Explain the need for, and use of, registers in the functioning of the processor

A register is a small area of the memory, within the processor itsel, where data or control information is temporarily stored

Registers are used because transferring data to and from a register is much quicker than transferring the data between the processor and main memory

PROGRAM COUNTER

Stores the address of the next instruction

Controls the sequence in which instructions are executed

It is incremented after being read

It is altered as a result of a jump instruction

MEMORY ADDRESS REGISTER (MAR)

Stores the address in memory currently being accessed. Holds the position in memory of the location containing either the next piece of data to be read or the next instruction to be used.

MEMORY DATA REGISTER (MDR)

Stores the data being transfered to or from memory

Acts like a buffer between IAS and CPU

CURRENT INSTRUCTION REGISTER (CIR)

Stores the instruction currently being operated on

ACCUMULATOR

Temporary store for the results of the last arithmetic or logical operation until it is decided what to do with the data

c. Explain the need for, and describe the use of buses to convey information

ADDRESS BUS

Carries identification about where the data is being sent/coming from

Necessary if large amounts of memory need to be used

DATA BUS

Carries data being transmitted between areas of the processor

Two-way bus as data can be transferred in either direction

CONTROL BUS

Carries control signals from the control unit to allow synchronisation fo signals

d. Describe the connectivity of devices

HARD WIRING

Fibre optic Cable - Transmits data using light beams sent down a fine glass filament AND Inteference free

WIRELESS CONNECTIONS

Wireless System - Used over short distances and not secure because anyone can tap in system

Microwave transmission

Use of satellite dishes,

Line of sight necessary and Used by businesses to connect a network in different locations

Infrared transmission - Unobstructed line of sight

Serial, parallel, duplex, half-fuplex data transmission

e. Describe the differences between types of primary memory and explain their uses

ROM (READ ONLY MEMORY)

Description

- Non-volatile

- Contents of memory are not erased when power is off

- Memory contents cannot be altered/changed

Types of software stored

- Contains the boot program (start-up software)

Reason

- Program is required immediately when power is switched on

- Therefore the boot program must be in ROM

RAM (RANDOM ACCESS MEMORY)

Description

- Volatile

- Contents of memory is erased when power is off

- Processor must have some RAM as working memory/buffer

Types of software stored

- Applications software, Operating System, User files

Reason

- Allows changes to be made to saved contents

- Allows changes to be made to files in current use/user can enter data

- Fast access to data

f. Describe the basic features, advantages, disadvantages and uses of secondary storage media

SECONDARY STORAGE DEVICES

Peripheral/external device which allows storage of data over a long period

Hard disk drive (HDD) - Magnetic medium

- Used for storing software including OD, other systems software, applications programs and data files

- Fast access to data

- Large capacity

- However requires formatting before use

CD-ROM (Optical Medium)

- Uses reflection of a laser off a pitted surface to store information

- Stores significant quantities of information

- Completely portable from one machine to another

- However access to information is slower

- CD-ROM cannot be altered/chaged by the user

- E.g. to load software such as Encyclopaedias

CD-RW (Optical Medium)

- Same as CD-ROM except

- Contents can be both erased and rewritten

- used to make backup files

- used for transporting files

DVD-ROM and DVD-RW (Optical Medium)

- Same as CD-ROM and CD-RW except...

- Hold larger amounts of information

- Faster access to information

Memory USB Stick (Solid State Medium)

- Useable on any machine

- Very fast access to information

- Device is fully portable, small and light

- No moving parts and are therefore more suitable for carrying around

- Large capacity

- Used to store sensitive information as device can be kept with owner

- Can be used to transport files

- Can be used to make backups

g. Describe the transfer of data between devices and primary memory, including the uses of buffers and interrupts

A buffer is a temporary storage that is used to hold data while it is being moved from the primary memory to a storage device

An interrupt is a message sent to the processor telling it to 'wait' whilst another more important command is executed.

- Data is sent to buffer from primary memory

- Processor can continue other tasks while data is transmitted

- Interrupt is sent when the buffer is full

- Buffer is emptied to the storage device but at a slower speed to accomadate the device

- When the buffer has been emptied, an interrupt is sent to the processor to request bugger refill

Continued...

...

- Process is repeated until the file of data has been successfully and fully transferred to the storage device

- Data is arranged in packets and sent via parallel communication

- Data is checked for errors on arrival at storage device

- If there are any errors, data would be resent

h. Describe a range of common peripheral devices in terms fo their features, advantages, disadvantages and uses

PERIPHERAL

Hardware device that is external to the computer but can be attached to the ocmputer

PRINTERS

Provides a permanent output as a hard copy and can be kept for alter use

E.g. proving evidence for updating other files

Advantages of sharing printers on a network

- More than one printer in case of failure

- Ease of maintenance

- Each user has access to different types of printers for different jobs

Disadvantages of sharing printers on a network

- Need to queue for printout

- Printouts are not private and printer may not be local

- There would be no direct control over printer and lack of backup if printer fails

PLOTTER

Type of printer designed for drawing lines and geometric designs

Image created by pens begin moved across a piece of paper, used for drawing blueprints, e.g. etailed drawings of building

ACTUATOR

Output device operated by a computer which produces and controls physical movement, e.g. in rolling process, actuator used to adjust gap between rollers

MICROPHONE

Instructions or data can be read into computer

SPEAKERS

Used to output sound from a computer system, Tells user what the computer has processsed, Useful for visually impaired people instead of monitors