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GATE CSE 2021 Set 2 Q30: DMA cycle stealing: device data rate from 0.5% of cycles

Question

Consider a computer system with DMA support. The DMA module is transferring one 8-bit character in one CPU cycle from a device to memory through cycle stealing at regular intervals. Consider a 2 MHz processor. If 0.5% processor cycles are used for DMA, the data transfer rate of the device is ________ bits per second.

Try it: numerical answer: type the value

Numerical answer. No negative marking.
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Answer: 80000 (official GATE 2021 final answer key)

Concept used: Each stolen cycle moves one 8-bit character.

First step: Stolen cycles per second =0.005×2×106= 0.005 \times 2 \times 10^6; multiply by 8 bits per cycle.

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Source: official GATE 2021 Set 2 CS question paper and final answer key, organised by IIT Bombay. Question paper · Answer key

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