Disk scheduling refers to the algorithms used by the operating system to manage the order in which read and write requests to the disk are processed. These algorithms aim to minimize seek time, which is the time taken for the disk's read-write head to move to the correct track.
The commonly used disk scheduling algorithms include:
1. **First Come First Serve (FCFS)**
- Processes requests in the order they arrive.
- Simple but can lead to high seek times if requests are scattered across the disk.
2. **Shortest Seek Time First (SSTF)**
- Selects the request closest to the current position of the read-write head.
- Minimizes seek time, but can cause starvation if requests for distant cylinders are continuously delayed.
3. **SCAN (Elevator Algorithm)**
- The disk head moves in one direction, servicing requests until it reaches the end, then reverses direction.
- It scans back and forth across the disk, ensuring fairness and reducing seek times compared to FCFS.
4. **C-SCAN (Circular SCAN)**
- Similar to SCAN, but the head moves in one direction and, after reaching the end, returns to the beginning without servicing any requests on the return trip.
- Provides more uniform wait times.
5. **LOOK**
- A variant of SCAN, but the head only goes as far as the last request in each direction, instead of going to the end of the disk.
6. **C-LOOK**
- Similar to C-SCAN, but the head moves only as far as the last request before reversing direction, then jumps back to the first request.
These algorithms balance efficiency and fairness, aiming to reduce the total seek time and optimize disk performance.
