GATE CS 2024 Set 1 | Question 15

MCQ · 1 mark · −0.33

Which one of the following statements is FALSE?

  1. Option A: In the cycle stealing mode of DMA, one word of data is transferred between an I/O device and main memory in a stolen cycle
  2. Option B: For bulk data transfer, the burst mode of DMA has a higher throughput than the cycle stealing mode
  3. Option C: Programmed I/O mechanism has a better CPU utilization than the interrupt driven I/O mechanism (correct)
  4. Option D: The CPU can start executing an interrupt service routine faster with vectored interrupts than with non-vectored interrupts

Answer

(C)

Explanation

Statement C is false. In programmed I/O the CPU keeps polling the device status until it is ready, so its cycles are wasted in busy-waiting. Interrupt-driven I/O lets the CPU do other work and respond only when the device raises an interrupt, so it gives better CPU utilization, not worse.

The other statements are true:

  • A: in cycle stealing, the DMA controller takes the bus for one cycle and moves one word.
  • B: burst mode keeps the bus for the whole block, so bulk transfers finish sooner.
  • D: a vectored interrupt supplies the address of its service routine, so the CPU need not poll devices to find the source.

Answer: C