Answer:
Given Data:
Rotation Speed = 7200 rpm
No. of tracks on one side of platter = 30000
No. of sectors per track = 600
Seek time for every 100 track traversed = 1 ms
To find:
Average Seek Time.
Average Rotational Latency.
Transfer time for a sector.
Total Average time to satisfy a request.
Explanation:
a) As given, the disk head starts at track 0. At this point the seek time is 0.
Seek time is time to traverse from 0 to 29999 tracks (it makes 30000)
Average Seek Time is the time taken by the head to move from one track to another/2
29999 / 2 = 14999.5 ms
As the seek time is one ms for every hundred tracks traversed. So the seek time for 29,999 tracks traversed is
14999.5 / 100 = 149.995 ms
b) The rotations per minute are 7200
1 min = 60 sec
7200 / 60 = 120 rotations / sec
Rotational delay is the inverses of this. So
1 / 120 = 0.00833 sec
= 0.00833 * 100
= 0.833 ms
So there is 1 rotation is at every 0.833 ms
Average Rotational latency is one half the amount of time taken by disk to make one revolution or complete 1 rotation.
So average rotational latency is: 1 / 2r
8.333 / 2 = 4.165 ms
c) No. of sectors per track = 600
Time for one disk rotation = 0.833 ms
So transfer time for a sector is: one disk revolution time / number of sectors
8.333 / 600 = 0.01388 ms = 13.88 μs
d) Total average time to satisfy a request is calculated as :
Average seek time + Average rotational latency + Transfer time for a sector
= 149.99 ms + 4.165 ms + 0.01388 ms
= 154.168 ms
