Algorithm
Step 1: Let the Request array represents an array storing indexes of tracks that have been requested. ‘head’ is the position of the disk head.
Step 2: Find the positive distance of all tracks in the request array from the head.
Step 3: Find a track from the requested array which has not been accessed/serviced yet and has a minimum distance from the head.
Step 4: Increment the total seek count with this distance.
Step 5: Currently serviced track position now becomes the new head position.
Step 6: Go to step 2 until all tracks in the request array have not been serviced.
Example:
Request sequence = {176, 79, 34, 60, 92, 11, 41, 114}
Initial head position = 50
The following chart shows the sequence in which requested tracks are serviced using SSTF.
Therefore, the total seek count is calculated as:
SSTF (Shortest Seek Time First)
= (50-41)+(41-34)+(34-11)+(60-11)+(79-60)+(92-79)+(114-92)+(176-114)
= 204
which can also be directly calculated as: (50-11) + (176-11)
Program for SSTF Disk Scheduling Algorithm
Given an array of disk track numbers and initial head position, our task is to find the total number of seek operations done to access all the requested tracks if Shortest Seek Time First (SSTF) is a disk scheduling algorithm is used.
The basic idea is the tracks that are closer to the current disk head position should be serviced first in order to minimize the seek operations is basically known as Shortest Seek Time First (SSTF).