Which one of the following statements is FALSE?
2024
Which one of the following statements is FALSE?
Answer: C. Programmed I/O mechanism has a better CPU utilization than the interrupt driven I/O mechanism — Answer: The false statement is: Programmed I/O mechanism has a better CPU utilization than the interrupt driven I/O mechanism. Cycle-stealing DMA: True — the…
- 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
- B.
For bulk data transfer, the burst mode of DMA has a higher throughput than the cycle stealing mode
- C.
Programmed I/O mechanism has a better CPU utilization than the interrupt driven I/O mechanism
- D.
The CPU can start executing an interrupt service routine faster with vectored interrupts than with non-vectored interrupts
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Correct answer: C
Answer: The false statement is: Programmed I/O mechanism has a better CPU utilization than the interrupt driven I/O mechanism.
Cycle-stealing DMA: True — the DMA controller steals individual memory cycles to transfer one word per stolen cycle, momentarily pausing the CPU for each transfer.
Burst-mode DMA: True — burst mode transfers a block of consecutive words in one continuous transfer, giving higher throughput for bulk data than repeatedly stealing single cycles.
Programmed I/O vs interrupt-driven I/O: The programmed I/O claim is false. Programmed I/O requires the CPU to poll the device or wait actively, consuming CPU cycles and reducing CPU utilization. Interrupt-driven I/O lets the CPU run other tasks and responds only when the device signals completion, improving CPU utilization.
Vectored vs non-vectored interrupts: True — vectored interrupts provide the service routine address directly, so the CPU can begin the interrupt service routine faster than when additional steps are required to identify the source.
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