Why the CPU execute faster than the input and output device?

Answer 1

The CPU is incredibly fast at executing data. The only problem is getting data to the CPU.

This arduous task is carried out by the various buses -

The control bus is a line which the CPU sends information about what device it wishes to communicate with

The data bus carries the actual data

The address bus carries memory locations.

This means that the I/O device has to do the following:

1. Inform the CPU that it wishes to talk. (It does this via IRQ [Interrupt Request] channels)

2. The CPU will inform the device that it is ready to talk through the Control bus.

3. The device will set its' ready signal to 0, meaning that it is sending data, then it will put the data on the data bus.

4. The CPU will receive the data, storing it in registers.

5. The device, once it has finished, will set the ready line to 1.

6. The CPU will read and execute the data, performing whatever is necessary.

7. The CPU will inform the device that it has finished

8. Then, if necessary, the CPU will pass any data back along the data bus, setting the data bus ready line to 0.

The main drawback is this: Only one device may use these buses at any one time. The CPU is far faster at doing the actual execution than it is to actually get all of the necessary instructions to the CPU.

I hope that answered your question.