SCAN Disk Scheduling Algorithm

The SCAN disk scheduling algorithm is another type of disk scheduling algorithm. In this algorithm, we move the disk arm into a specific direction (direction can be moved towards large value or the smallest value). Each request is addressed that comes in its path, and when it comes into the end of the disk, then the disk arm will move reverse, and all the requests are addressed that are arriving in its path. Scan disk scheduling algorithm is also called an elevator algorithm because its working is like an elevator.

Advantages of SCAN Disk Scheduling Algorithm

In SCAN disk scheduling, there is a low variance of response time.
In this algorithm, throughput is high.
Response time is average.
In SCAN disk scheduling, there is no starvation.

Disadvantages of SCAN Disk Scheduling Algorithm

SCAN disk scheduling algorithm takes long waiting time for the cylinders, just visited by the head.
In 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 SCAN scheduling.