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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

1 Answer

Best answer
12 votes
12 votes
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
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