Higher Computing Science Interfaces

2. Interfaces
 A peripheral sends and/or receives data at a certain speed and using a
certain format.
 The CPU and/or the device receives data at a certain speed and using a
certain format.
 An interface is a unit that sits between the CPU and a peripheral device and
compensates for the differences in speed, codes etc. to ensure compatibility.
COMPUTERDEVICE INTERFACE

3. Status Information
 The interface can provide information on the status of the peripheral
 Printer – ready / out of paper / jam
 Network – data sent and received
 MIDI – data received

4. Data Conversion
 A CPU will work with data using different formats and speeds than
peripherals
 For example, the processor will be able to send data to the printer at a speed
faster than printer can handle it
 Data may be sent / received in serial or parallel format
Parallel Serial

5. Protocol
The processor and peripheral require a set of rules so that they know how to
communicate with each other. These rules are known as a protocol.
The protocol will include:
the type of error checking to be used
data compression method, if any
how the sending device will indicate that it has finished sending a message
how the receiving device will indicate that it has received a message

6. Data Storage
What happens if the processor wants to send/receive data to/from a peripheral
which handles data at a different speed?
e.g. a printer can only print 5 pages per minute
A hard drive can only write at 70 megabytes per second
A microphone captures data at a speed faster than the processor can
process it

7. Data Storage
What happens if the processor wants to send/receive data to/from a peripheral
which handles data at a different speed?
e.g. a printer can only print 5 pages per minute
A hard drive can only write at 70 megabytes per second
A microphone captures data at a speed faster than the processor can
process it
In cases like this, the problem would be that the processor or peripheral would
have to wait until the job was finished unable to carry out any other tasks.

8. Data Storage
What happens if the processor wants to send/receive data to/from a peripheral
which handles data at a different speed?
e.g. a printer can only print 5 pages per minute
A hard drive can only write at 70 megabytes per second
A microphone captures data at a speed faster than the processor can
process it
In cases like this, the problem would be that the processor or peripheral would
have to wait until the job was finished unable to carry out any other tasks.
Buffers and spoolers provide the solution to this problem

9. Buffer
A buffer is an area of computer memory that is allocated to transferring data
between the computer and a peripheral.
A buffer will be used when a fast acting part of the system is exchanging data
with a slow acting device eg a printer

10. Buffer
Most interfaces have buffers to store blocks of data while in transfer between
the processor and the peripheral.
This ensures that the processor is not held up by slow communications to and
from the peripherals.
The buffer must also keep the status of the peripheral so that the processor
knows when it is able to send or receive data and when problems arise.

11. Spooler
Another approach to ensuring the processor is not held up by slow peripherals
is to send data to be spooled.
This means that the data is sent to fast backing storage (usually the hard disk).
Data is then sent from the backing store to the peripheral in the gaps between
processing actions (an example of this is background printing).

12. Spooler
The user can continue operating the computer while the data is being sent to
the peripheral.
This is preferred to buffering when large amounts of data is to be sent or if the
peripheral is shared across a network.