A processor is fetching instructions at the rate of 1 MIPS. A DMA module is…

2013

A processor is fetching instructions at the rate of 1 MIPS. A DMA module is used to transfer characters to RAM from a device transmitting at 9600 bps. How much time will the processor be slowed down due to DMA activity?

  1. A.

    9.6 ms

  2. B.

    4.8 ms

  3. C.

    2.4 ms

  4. D.

    1.2 ms

Attempted by 70 students.

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Correct answer: D

First, convert the transmission rate to characters per second. Assuming 8-bit characters, 9600 bps equals 1200 characters per second (9600 / 8). The processor operates at 1 MIPS, which is 1,000,000 instructions per second. If the DMA transfer consumes one instruction cycle per character, the processor spends 1200 cycles out of every 1,000,000 on DMA activity. This results in a slowdown of 1200 / 1,000,000 = 0.0012 seconds per second of operation. Converting to milliseconds, the processor is slowed down by 1.2 ms.

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