How is Average Seek Time Calculated?
A hard disk system has the following parameters :
Number of tracks = 500
Number of sectors/track = 100
Number of bytes /sector = 500
Time taken by the head to move from one track to adjacent track = 1 ms
Rotation speed = 600 rpm.
What is the average time taken for transferring 250 bytes from the disk ?
Well I wanted to know How the average seek time is calculated ?
My Approach
Avg. time to transfer = Avg. seek time + Avg. rotational delay + Data transfer time
Avg Seek Time
given that : time to move between successive tracks is 1 ms
time to move from track 1 to track 1 : 0ms
time to move from track 1 to track 2 : 1ms
time to move from track 1 to track 3 : 2ms
..
..
time to move from track 1 to track 500 : 499 ms
Avg Seek time =
= 249.5 ms
But After Reading Answer given here Why is average disk seek time one-third of the full seek time?
Im confused with my approach.
My question is
Is my Approach Correct ?
- If not Please explain the correct way to calculate Average seek time
- If Yes please explain wh we are not considering average for every possible pair of tracks (as mentioned in the above link)?
Answer
There are a lot more than 500 possible seek times. Your method only accounts for seeks starting at track 1.
What about seeks starting from track 2? Or from track 285?
I wouldn't say your approach is wrong, but it's certainly incomplete.