Which of the following DMA transfer modes and interrupt handling mechanisms…
2006
Which of the following DMA transfer modes and interrupt handling mechanisms will enable the highest I/O band-width?
- A.
Transparent DMA and Polling interrupts
- B.
Cycle-stealing and Vectored interrupts
- C.
Block transfer and Vectored interrupts
- D.
Block transfer and Polling interrupts
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Correct answer: C
Answer: Block transfer and Vectored interrupts enable the highest I/O bandwidth.
Why this combination is best:
Block transfer (burst mode): transfers a whole block in consecutive bus cycles, minimizing handshake and per-word overhead and maximizing raw bus utilization.
Vectored interrupts: provide the CPU with the address of the correct interrupt service routine so servicing starts immediately, reducing latency and CPU overhead per interrupt.
Comparing the alternatives:
Cycle-stealing interleaves DMA and CPU usage by taking small numbers of cycles repeatedly, which increases the total transfer time compared with a single burst and reduces effective throughput.
Transparent DMA only transfers during CPU idle times, so throughput depends on CPU idle slots and is typically lower than dedicated burst transfers.
Polling forces the CPU to check device status repeatedly, wasting CPU cycles and increasing effective interrupt overhead compared with vectored interrupts.
Combined effect: block transfers maximize bus throughput while vectored interrupts minimize CPU and interrupt handling overhead, producing the highest sustained I/O bandwidth.