The size of the data count register of a DMA controller is 16 bits. The…
2016
The size of the data count register of a DMA controller is 16 bits. The processor needs to transfer a file of 29,154 kilobytes from disk to main memory. The memory is byte addressable. The minimum number of times the DMA controller needs to get the control of the system bus from the processor to transfer the file from the disk to main memory is _________ .
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Correct answer: 456
Key insight: the 16-bit data count register limits a single DMA transfer to 2^16 = 65,536 bytes when memory is byte-addressable.
Convert the file size to bytes: 29,154 KB = 29,154 × 1024 = 29,853,696 bytes.
Maximum bytes per DMA bus acquisition = 65,536 bytes.
Number of times DMA must gain the bus = ceil(29,853,696 / 65,536) = ceil(455.5...) = 456.
Answer: 456
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