Consider a disk queue holding requests to the following cylinders in the listed order: 116, 22, 3, 11, 75, 185, 100, 87. Using the SCAN scheduling algorithm, what is the order that the requests are serviced, assuming the disk head is at cylinder 88 and moving upward through the cylinders?
A) 116 - 22 - 3 - 11 - 75 - 185 - 100 - 87
B) 100 - 116 - 185 - 87 - 75 - 22 - 11 - 3
C) 87 - 75 - 100 - 116 - 185 - 22 - 11 - 3
D) 100 - 116 - 185 - 3 - 11 - 22 - 75 - 87

Question

Quizplus · Accepted Answer

The SCAN scheduling algorithm services requests in the order of their placement on the disk queue, but always in the direction of the closest end of the disk. Since the disk head is moving upward through the cylinders, it will first service the requests that are above the current position on the disk (from 88 to 100), then it will reverse direction and service the requests below the current position on the disk (from 75 to 3). Therefore, the correct order of service for this disk queue using SCAN scheduling algorithm would be: 
100 - 116 - 185 - 87 - 75 - 22 - 11 - 3.

Consider a Disk Queue Holding Requests to the Following Cylinders