GATE CS 2008 Q64 — I/O Interface: Interrupt and DMA Mode

To determine which statement is NOT true, let us analyze the behavior of synchronous and asynchronous I/O:

• Synchronous I/O: The calling process blocks (waits) until the I/O operation completes. Once the hardware device finishes, it generates an interrupt that invokes an Interrupt Service Routine (ISR). The ISR processes the data and wakes up the blocked process. Thus, statements C and D are true.
• Asynchronous I/O: The calling process does not block and continues its execution. The completion of the I/O can be handled via polling (checking status registers) or non-interrupt mechanisms like direct memory access (DMA) completion signals. Since a traditional ISR is not strictly required to wake up a waiting process, statement A is considered true.

Consequently, statement B, which claims that an ISR is invoked in both synchronous and asynchronous I/O, is NOT true.