File and Input/Output System Q.32

32If a disk has a seek time of 20 ms, rotates 20 revolutions per second, has 100 words per block, and each track has capacity of 300 words. Then the total time required to access one block is

Option : D
Explanation : Time taken to access one block = seek time + rotational delay + block transfer time
Seek time = 20 ms (given)
Rotational delay = on an average taken to be the time to rotate by half = 1/2 X time for 1 rotation = 1/2 X 1/20 seconds = 1/40 s = 25 ms
Block Transfer time = block size / transfer rate = 100 / transfer rate
Now, transfer rate = Track capacity / rotation rate = 300 / ( 1/ 20) = 6000 word per sec = 6 word per ms
Block Transfer time = block size / transfer rate = 100 / 6 ~ 16.67 ms per block Time taken to access one block = seek time + rotational delay + block transfer time= 20 + 25 + 16.67 = 61.67 ms

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