Standard algorithms apply, adapted to the special situation :
FCFS
Easiest to implement, but: may require lots of head movements.
Shortest Seek Time First
Select job with minimal head movement
Problems:
- may cause starvation
- Tracks in the middle of disk preferred
Algorithm does not minimise number of head movements
SCAN scheduling
Head continuously scans the disk from end to end (lift strategy)
solves the fairness and starvation problem of SSTF
Improvement : LOOK-scheduling :
head only moved as far as last request (lift strategy).
Particular tasks may require different disk access algorithms
Example
Swap space management
Speed absolutely crucial different treatment :
- Swap space stored on separate partition
- Indirect access methods not used
- Special algorithms used for access of blocks Optimised for speed at the cost of space (e.g., increased internal fragmentation)