Review  various Disk scheduling algorithms

There are  kinds of disk scheduling algorithms

1. FCFS scheduling

In the FCFS scheduling, we treat each disk position search in the order of their arriving sequence. It's very simple, since we only need to go to each position of the disk one by one.



2. SSTF scheduling

In the SSTF scheduling ( shortest-seek-time-first) algorithm, we do the search depends on the distance of the position from the current postition. Every time we decide which position in the queue to go, we will check all the queue to see which position is the cloest one from the current position.



3.  SCAN scheduling

In the scan scheduling algorithm, we dont care about the sequence. This algorithm indicates that, we will choose a direction from the current position, then we go to the end of the disk range, if we reach the end of the disk, then we turn around and go to the end of another direction. In the path, we will visit every position required in the queue.



4.C-SCAN scheduling

The only difference between C-SCAN and SCAN is that C-SCAN will jump to the another end of the disk and start scan in the same direction.



5. LOOK scheduling

The only difference between LOOK and SCAN is the range of scan. In LOOK algorithm, we willl go throuth the queue first to find the maximum and minimum postition, then we dont have to go to the end of the disk. We will turn around when reaching our range.