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Consider the following disk request sequence for a disk with 100 tracks.

98, 183, 37, 122, 14, 124, 65, 65, 67

Head pointer starting at 53 (current position of R/W heads) and moving in left direction.Find the number of head movements in cylinders using SCAN scheduling.

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In SCAN Scheduling,the disk arm starts at one end of the disk,and moves towards the other end,servicing requests until it gets to the other end of the disk,where the head movement is reversed and servicing continues.

Here in this question,R/W head is at  53 position and moving in left direction so it will serve all the requests till 14.

Take a look.

53-->37

37-->14

Now it will reach the end of the disk so this will also be a track movement.

14-->0

Again again it will start servicing the request in opposite direction.

0-->65

65-->67

67-->98

98-->122

122-->124

124-->183.

So,total head movements will be 236.

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