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Disk requests come to a disk driver for cylinders in the order 10, 22, 20, 2, 40, 6 and 38 at a given time when the given disk drive is reading from cylinder 20. The seek time is 6ms per cylinder.

1.What is the total seek time, if the disk arm scheduling algorithm FCFS is used?

A)360 ms        B)850 ms      C)900 ms        D)None

2.What is the total seek time, if the closest cylinder next scheduling is used?

A)360 ms        B)876 ms      C)850 ms        D)900 ms
asked in Operating System by Loyal (6.1k points) | 3.4k views

1 Answer

+8 votes
Best answer
1. FCFS
Total seek time
= 10*6 + 12*6 + 2*6 + 18*6+ 38 * 6 + 34*6 + 32*6
= 146*6
= 876 ms

2. Closest cylinder next:
Here the service order will be
20 22 10 6 2 38 40
So, total seek time
= (0 + 2 + 12 + 4 + 4 + 36 + 2) * 6
= 60 * 6
 = 360
answered by Veteran (358k points)
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0
Arjun sir I have small doubt please clear
Sir they mention that when the disk drive is reading from cylinder 20 so in fcfs before 20 10 and 22 comes so why you consider it they are already served...

So please clear my doubt where I am wrong
0
Seek time means the time required to move the read/write head from one cylinder to another cylinder ....so suppose in order to move from cylinder number 22 to 20..here the read/write head has to be moved from 22 to 21 and then 21 to 20...so here to move from 22 to 20 12msec is required.....


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