Mumbai University > Electronics Engineering > Sem6 > Computer Organization

Marks: 10M

Year: May 2015

The different I/O access methods are as shown below:-

1) Single Bus Scheme:-

• Here, both the CPU and I/O module (I/O processor) share the same bus.

• Such a multiprocessor system is also called as “Closely coupled” system.

• Advantage:

  a) Such systems are cheap and easy to implement.

  b) They are best suited for a uni-processor environment.

• Disadvantage:

  a) In multiprocessor systems, having only one processor can be the bus master at a time. So when one processor is using the bus the other processor will have to wait.

  b) Reliability of the system is very poor. If the bus fails then the entire system will stop working.

2) Dual Bus Scheme:-

• Here, both the CPU and the I/O module have individual buses.

• The CPU carries out its memory operations on the system bus, and the I/O processor has a dedicated I/O bus for its I/O operations.

• Such a multiprocessor system is called “loosely coupled system”.

• Advantage:

  a) They are best suited for multiprocessor environment.

  b) Performance of the system is better as both processors can use their buses simultaneously.

  c) Reliability of the system is better.

Even if the I/O bus fails, CPU carries out its operation on the system bus.

• Disadvantage:

  a) Cost of the systems which have a lot of processors.

  b) System is complex to implement.

3) Multiple Bus Scheme:-

• This is used in systems which have a lot of processors.
• Each processor is provided with a dedicated bus and all processors are interleaved on a network.
• Such systems are extremely powerful and fault resistant, but are costly and complex. The various way of connecting them are dedicated link, crossbar, hypercube etc.