Correct Answer - Option 2 : 0.75 sec
The correct answer is 0.75 sec.
Average seek time for a random location time is given as 10 ms. The average rotational latency is half of the time needed for complete rotation. It is given that 6000 rotations need 1 minute. So one rotation will take 60/6000 seconds which is 10 ms. Therefore average rotational latency is half of 10 ms, which is 5ms.
Average disk access time = seek time + rotational latency
= 10 ms + 5 ms = 15 ms
For 50 libraries, the average disk access time will be 15*50 ms =750ms
1 sec = 1000 ms
750 divide the time value by 1000 =0.75
Therefore option 2 is correct