Question

A hard disk with a transfer rate of 10 mbytes/ second is constantly transferring data to memory using dma. The processor runs at 600 mhz, and takes 300 and 900 clock cycles to initiate and complete dma transfer respectively. If the size of the transfer is 20 kbytes, what is the percentage of processor time consumed for the transfer operation ?

Answer 1

Clock cycle time = 1600×106 [ Frequency = 1/Time]

For DMA initiation and completion = (900+300)600×106=2 microsec .

Disk Transfer rate =10 Mbytes/sec

1 byte =1107 sec

20 Kbytes =2 milisec =2000 micro sec

Percentage =(22+2000)×100=0.0999≃0.1%

option (D)

% of CPU time consume xx+y

Now, when, use x= Data preparation time or Total cycle time used by CPU and y= Data transfer time

To calculate the fraction of CPU time to the data transfer time - we use xx+y it is burst mode.

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