1.FCFS Scheduling

If the early ready process is ahead of the ready queue and the late ready process is behind the ready queue, FCFS (first come first service) always schedules the process currently at the top of the ready queue to the running state.

2.SSTF Scheduling

SSTF(Shortest Seek Time First) This algorithm selects such a process, which requires that the track to be accessed is closest to the track where the current head is located, so as to minimize the seek time each time. However, this scheduling algorithm cannot guarantee the shortest average seek time. The average moving distance of SSTF is significantly lower than that of FCFS. SSTF has better seek performance than FCFS, so it has been widely used in the past.

3.SCAN Scheduling

The head only scans in one direction, and completes all incomplete requests in the scanning process, until the head reaches the last track of the disk in this direction or the track of the last request in this direction.

4.C-SCAN Scheduling

On the basis of the disk scanning algorithm, change the scanning path of the head: after scanning to the innermost layer, continue scanning from the outermost layer to the inside, that is, the scanning direction is the same. The idea of the algorithm is basically the same as that of the scanning algorithm, and the two-dimensional array is also used to store the process number and the track number of the process. The difference of the algorithm is that when the head scans to the innermost layer of the disk, the head jumps to the outermost layer of the disk and scans inward again, so as to effectively avoid rescanning the scanned tracks once again and reduce the average search distance 。

5.LOOK Scheduling

The improvement of scan algorithm and C-scan algorithm, that is, the head movement only needs to reach the farthest request to return, and does not need to reach the disk endpoint. This form of scan algorithm and C-scan algorithm is called look and c-look scheduling. This is because they look for requests before moving in a given direction.