In SCAN algorithm the disk arm moves into a particular direction and services the requests coming in its path and after reaching the end of disk, it reverses its direction and again services the request arriving in its path. So, this algorithm works as an elevator and hence also known as elevator algorithm. As a result, the requests at the midrange are serviced more and those arriving behind the disk arm will have to wait.

Characteristics of SCAN :

The disk arm starts to scan all the requests in a direction and reaches the end of the disk.
After that, it reverses its direction and starts to scan again the requests in its path and serves them working like an elevator.

Advantages of SCAN :

High throughput
Low variance of response time
Average response time

Disadvantages of SCAN :

Long waiting time for requests for locations just visited by disk arm.