GATE | GATE CS 2008 | Question 64

Which of the following statements about synchronous and asynchronous I/O is NOT true?
(A) An ISR is invoked on completion of I/O in synchronous I/O but not in asynchronous I/O
(B) In both synchronous and asynchronous I/O, an ISR (Interrupt Service Routine) is invoked after completion of the I/O
(C) A process making a synchronous I/O call waits until I/O is complete, but a process making an asynchronous I/O call does not wait for completion of the I/O
(D) In the case of synchronous I/O, the process waiting for the completion of I/O is woken up by the ISR that is invoked after the completion of I/O

Answer: (B)

Explanation: An interrupt service routine will be invoked after the completion of I/O operation and it will place process from block state to ready state, because process performing I/O operation was placed in blocked state till the I/O operation was completed in Synchronous I/O.

However, process performing I/O will not be placed in the block state and process continues to execute the remaining instructions in Asynchronous I/O, because handler function will be registered while performing the I/O operation, when the I/O operation completed signal mechanism is used to notify the process that data is available.

So, option (B) is false.

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