Computer Systems

Nat 4/5 Computing Science

Interfaces & Peripherals

Lesson Aims By the end of this lesson: Pupils at Nat 5 level will be able to:

Describe the need for and purpose of interfaces

Identify the interface used on a specific device Identify the speed(transfer rate) of an interface

Describe the functions of an interfaceCompensating for differences in speed between

the CPU and peripheralsData conversion from analogue to digital forms

and Temporary data storage

Peripherals How many of you have connected a

device (peripheral) to your computer? USB Flash Drive Mobile Phone/Ipod? Printers/Scanners?

You have either connected these using wires or wirelessly. But they have all connected using an interface

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Interface An interface can be described as:

Boundary across which two systems communicate

This is the piece of equipment that allows your scanner to communicate with the PC or for the pc to send information to the printer. The devices may speak different languages

and work differently. So the interface’ main role is to deal with

this

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Interface- Functions

•When there are differences in speed

Compensating for differences in

speed between the CPU and

peripherals

•Some devices work with data in different forms

Data conversion from analogue to digital forms

•Sometimes data that is being transferred needs to be stored

Temporary data

Storage

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Function: Compensation Compensating for differences in speed

between the CPU and peripherals Compare the processor of a computer and

an iPod? Computer CPU Speed: 2.5Ghz IPod CPU Speed: 800Mhz

If the computer tried to get the iPod to do instructions at the same rate as it could there would be a problem!

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Analogue and Digital As we have previously discussed

computers are digital machines. This means that there are only 2 signals.

A sample digital signal could look like

Analogue signals ( like our voice) are analogue – this means that they can be any value between a minimum and maximum.

Such as: -

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Function: Data Conversion Data conversion from analogue to digital

Remember Computers are digital machines!

However it may deal with analogue data, such as an input from a microphone or a analogue stick movement from a game controller

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Examples of Data Conversion

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Analogue Digital

AnalogueDigital

Function: Temporary Storage Another function of an interface is

temporary data storage This would happen when a computer is

trying to transfer data for example to a printer.

The computer is going to be able to send data to the printer far more quickly than the printer can process it.

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Function: Temporary Storage So the printers interface would have to

temporarily store the data Then allow the printer to process it at a rate

the printer could deal with.

This function is similar to using a funnel when filling a container with water.

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General Trends Transfer Speeds

USB has improved up to USB 3 12 Mbs up to 4.8Gbps

SATA is now on revision 3 1.5 Gbit/s up to 6Gbit/s

Wireless Wifi Bluetooth Infra Red (IR)

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Summary A device needs an interface to allow it to

communicate with a system

An interface has three main functions

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Compensating for differences in speed between the CPU and peripherals

Data conversion from analogue to digital forms

Temporary data Storage