Question

In a general purpose computer system the CPU, the main memory and the cache may be interconnected via one or more shared system bus(es). However, the secondary storage units (eg. Hard disk) will only be connected to the system bus through an I/O controller. The following are three statements regarding the requirement for an I/O controller

(i) The response times of I/O devices are very much slower than that of main memory and hence direct interfacing is impossible.
(ii) It is always better to off load the I/O processing to a secondary processor on the I/O controller board than to depend on the primary CPU for I/O processing.
(iii) The variety of I/O devices in the market require a separate I/O controller that exists for each device.

What statement(s) is/are true with reference to the requirement for an I/O controller? Justify your answer.

Answer 1

Answer (i)

True. I/O devices are very slower compared to CPU and memory so connecting them directly is not possible due to latency. I/O interface (controller) provides buffer (storage) and error detection mechanism for I/O devices.

Answer (ii)

True. I/O devices are slower in speed and because of that data needs to be buffered. That's why its better to have this processing on secondary CPU in I/O interface instead of CPU to save CPU time.

Answer (iii)

True. Each I/O device has different word length, data format etc. which can be understood by specific I/O interface only.