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Applied Test Series

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In a system SCAN, disk scheduling policy has been used. The number of tracks traversed by the head if the disk has 200 tracks and the requested tracks, in the order received, are 65, 48, 39, 08, 99, 164, 152, 38, 124

 

PS : Assume initial head position is at 65, and it will move towards 0

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SCAN is also called the Elevator Algorithm. In this algorithm, the disk arm moves into a particular direction till the end, satisfying all the requests coming in its path, and then it turns back and moves in the reverse direction satisfying requests coming in its path.

 

 

Number of tracks moved by the head

= [(65 - 48) + (48 - 39) + (39 - 38) + (38 - 8) + (8 - 0) + (99 - 0) + (124 - 99) + (152 - 124) + (164 - 152)]

= [17 + 9 + 1 + 30 + 8 + 99 + 25 + 28 + 12]

= 229

 

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in the scan  algorithm of deisk scheduling …. always head move from one end to another end and if and service in its path serve it  so here go from 65  to zero and after this 0 to last service 164  so overallhead movement is 229
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