1. Nat 4/5 Computing Science Interfaces & Peripherals
Computer Systems
Nat 4/5 Computing Science
Interfaces & Peripherals

2. 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 interface
Compensating for differences in speed between the CPU and peripherals
Data conversion from analogue to digital forms and
Temporary data storage

3. Nat 4/5
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

4. Interface An interface can be described as:
Nat 4/5
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

5. Interface- Functions When there are differences in speed
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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

6. Function: Compensation
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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!

7. Nat 4/5
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: -

8. Function: Data Conversion
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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

9. Examples of Data Conversion
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Examples of Data Conversion
Analogue
Digital
Digital
Analogue

10. Function: Temporary Storage
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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.

11. Function: Temporary Storage
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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.

12. General Trends Transfer Speeds Wireless USB has improved up to USB 3
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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)

13. Nat 4/5
Summary
A device needs an interface to allow it to communicate with a system
An interface has three main functions
Compensating for differences in speed between the CPU and peripherals
Data conversion from analogue to digital forms
Temporary data Storage