Question

Suppose that the head of a moving head disk with 200 tracks numbered 0 to 199 is currently serving a request at track 65.disk queue requests are as follows,93,173,132,20,35,150,100,175.What is the total number of head movements needed to satisfy these requests for the SCAN disk scheduling algorithm.

in SCAN,does it go to 199 or just till 175 on the right side.

for left side,does it go till 20 at the end or first 20 and at last 35..??

Answer 1

In SCAN we go from starting point to inside till zero and then go outside till the last request.

tracks 0 - 99

starting: 65

requests: 93,173,132,20,35,150,100,175,  after sorting: 20,35,93,100,132,150,173,175

servicing requests: 65 -> 35 -> 20 -> 0 -> 93 -> 100 -> 132 -> 150 -> 173 -> 175