Circular SCAN Disk Scheduling

Circular scanning works just like the elevator to some extent. It begins its scan toward the nearest end and works it way all the way to the end of the system. Once it hits the bottom or top it jumps to the other end and moves in the same direction. Keep in mind that the huge jump doesn't count as a head movement. The total head movement for this algorithm is only 187 track, but still this isn't the mose sufficient.

Advantages

Provides more uniform wait time compared to SCAN.

The waiting time for the cylinders just visited by the head is reduced as compared to the SCAN Algorithm.

It provides better response time.

Disadvantages

It causes more seek movements as compared to SCAN Algorithm.

It causes the head to move till the end of the disk even if there are no requests to be serviced.

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.