1. 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. 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 Nat 4/5

4. 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 Nat 4/5

5. 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 Nat 4/5

6. 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! Nat 4/5

7. 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: - Nat 4/5

8. 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 Nat 4/5

9. Examples of Data Conversion Nat 4/5

10. 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. Nat 4/5

11. 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. Nat 4/5

12. 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) Nat 4/5

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