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Consider a device that is to transfer data at a rate of 1 Mbytes/sec in 16bytes chunks. The overhead of polling is 400 cycles on 500 Mhz processor. Calculate the overhead of polling assuming I/O uses polling mechanism to transfer data?

A. 5%

B. 8%

C. 6%

D.4%
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Transfer rate = 1M Bytes/sec

16 bytes -  ?

1 sec = 1M Bytes

1 Bytes = 1/M sec

16 Bytes -- 16/1000000 sec = 16 *10^-6 sec = 16 micro sec.

sec = 1/hz

Cycle time = 1/500 *10^6 = 10^-6/ 500 sec

Polling overhead = 400 cycles * cycle time = (400*10^-6)/500 sec = 0.8micro sec

Polling overhead = 0.8 / 16  = 5 %
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