LOOK Disk Scheduling Algorithm

Look disk scheduling is another type of disk scheduling algorithm. Look scheduling is an enhanced version of SCAN disk scheduling. Look disk scheduling is the same as SCAN disk scheduling, but in this scheduling, instead of going till the last track, we go till the last request and then change the direction.

Advantages of LOOK Disk Scheduling Algorithm

  1. In Look disk scheduling, there is no starvation.
  2. Look disk scheduling offers low variance in waiting time and response time.
  3. Look disk scheduling offers better performance as compared to the SCAN disk scheduling.
  4. In look disk scheduling, there is no requirement of disk head to move till the end to the disk when we do not have any request to be serviced.

Disadvantages of LOOK Disk Scheduling Algorithm

  1. In look disk scheduling, there is more overhead to find the end request.
  2. Look disk scheduling is not used in case of more load.

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 LOOK scheduling. Number of cylinders crossed = 11 + 13 + 20 + 24 + 11 + 4 + 46 + 169 = 298