Question Details Consider a single-platter disk with the following parameters:ro

Question

Question Details
Consider a single-platter disk with the following parameters:rotation speed: 7200 rpm; number of tracks on one side ofplatter:30,000; number of sectors per track:600; seek time: one msfor every hundred tracks traversed. Let the disk receive a requestto access a random sector on a random track and assume the diskhead starts at track 0.
a) What is the average seek time?
b) What is the average rotational latency?
c) What is the transfer time for a sector?
d) What is the total average time to satisfy a request?

Explanation / Answer

a. If we assume that the head starts at track 0, then the calculations are simplified.

If the request track is track 0, then the seek time is 0; if the requested track is

track 29,999, then the seek time is the time to traverse 29,999 tracks. For a

random request, on average the number of tracks traversed is 29,999/2 =

14999.5 tracks. At one ms per 100 tracks, the average seek time is therefore

149.995 ms.

b. At 7200 rpm, there is one revolution every 8.333 ms. Therefore, the average

rotational delay is 4.167 ms.

c. With 600 sectors per track and the time for one complete revolution of 8.333 ms,

the transfer time for one sector is 8.333 ms/600 = 0.01389 ms.

d. The result is the sum of the preceding quantities, or approximately 154 ms.

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