Exercise 8. (OSC 10.11) (18%) Suppose that a disk drive has 5000 cylinders, numb

Question

Exercise 8. (OSC 10.11) (18%) Suppose that a disk drive has 5000 cylinders, numbered 0 to 4999. The drive is currently serving a request at cylinder 2150, and the previous request was at cylinder 1805. The queue of pending requests, in FIFO order, is: 2069, 1212, 2296, 2800, 544, 1618, 356, 1523, 4965, 3681. Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for each of the following disk-scheduling algorithms? ·FCFS ·SSTF SCAN LOOK o C-SCAN C-LOOK

Explanation / Answer

FCFS:
Order is - 2150,2069,1212,2296,2800,544,1618,356,1523,4965,3681
Distance are - 81+857+1084+504+2256+1074+1262+1167+3442+1284 = 13011 cylinder.

SSTF:
Order is - 2150,2069,2296,2800,3681,4965,1618,1523,1212,544,256
Distance are- 81+227+504+881+1284+3347+95+311+668+188= 7586 cylinder.

SCAN:
Order is - 2150,2296,2800,3681,4965,4999,2069, 1618,1523,1212,544,356
Distance are- 146+504+881+1284+34+2930+451+95+311+668+188=7492 cylinder.

LOOK:
Order is: 2150,2296,2800,3681,4965,2069,1618,1523,1212,544,256.
Distance are - 146+504+881+1284+2896+451+95+311+668+188=7424 cylinder

C-SCAN:
Order is: 2150,2296,2800,3681,4965,4999,0,356,544,1212,1523,1618,2069
Distance are - 146+504+881+1284+34+4999+356+188+668+311+95+451=9917 cylinder

C-LOOK:
Order is: 2150,2296,2800,3681,4965,356,544,1212,1523,1618,2069.
Distance are - 146+504+881+1284+4609+188+668+311+95+451= 9137 cylinder.

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