- Do all requests in the same Cylinder before moving on
- Want to move between close cylinders
- Want to do requests that are closest to the Write Head in the rotational time domain
- Disk scheduling used to be performed by the OS, now it is performed by the disk controller. All the OS does is enter the requests into a queue, which can be 31 length
FCFS
“First Come First Serve”
Do the requests in the order that they arrive in.
SSTF
“Shortest Seek Time First”
Perform the request that is closest to the head, i.e. has the shortest seek time.
LOOK
Go in the same direction until no more requests in that direction.
Works like a real elevator.
SCAN
LOOK, but always go to the top and bottom floors every trip.
So-called “elevator algorithm”, but LOOK is more deserving of the title
C-SCAN
SCAN, but you only service on the way up, then jump all the way to the bottom.
C-LOOK
LOOK, but you only service requests in one direction, then jump all the way over in the other direction.
