Circular LOOK Disk Scheduling

This is just an enhanced version of C-SCAN. In this the scanning doesn't go past the last request in the direction that it is moving. It too jumps to the other end but not all the way to the end. Just to the furthest request. C-SCAN had a total movement of 187 but this scan (C-LOOK) reduced it down to 157 tracks.

Advantages

It does not causes the head to move till the ends of the disk when there are no requests to be serviced.

It reduces the waiting time for the cylinders just visited by the head.

It provides better performance as compared to LOOK Algorithm.

It does not lead to starvation.

It provides low variance in response time and waiting time.

Disadvantages

There is an overhead of finding the end requests.

EXAMPLE : Lets say we are given with the following queue ==> 95, 180, 34, 119, 11, 123, 62, 64 with the Read-write head initially at the track 50 and the tail track being at 199 let us now discuss the different algorithms.