C-SCAN Disk Scheduling Algorithm

C-SCAN stands for Circular-SCAN. C-SCAN is an enhanced version of SCAN disk scheduling. In the C-SCAN disk scheduling algorithm, the disk head starts to move at one end of the disk and moves towards the other end and service the requests that come in its path and reach another end. After doing this, the direction of the head is reversed. The head reaches the first end without satisfying any request and then it goes back and services the requests which are remaining.

Advantages of C-SCAN Disk Scheduling Algorithm

  1. C-SCAN offers better uniform waiting time.
  2. It offers a better response time.

Disadvantages of C-SCAN Disk Scheduling Algorithm

  1. In C-SCAN disk scheduling, there are more seek movements as compared to SCAN disk scheduling.
  2. In C-SCAN disk scheduling, we have to move the disk head to the end of the disk even when we don’t have any request to service.

Example

Consider the following disk request sequence for a disk with 100 tracks 98, 137, 122, 183, 14, 133, 65, 78 Head pointer starting at 54 and moving in left direction. Find the number of head movements in cylinders using C-SCAN scheduling.

No. of cylinders crossed = 40 + 14 + 199 + 16 + 46 + 4 + 11 + 24 + 20 + 13 = 387