Name four disk-arm scheduling algorithms. Outline the basic algorithm for each.
Answer:
FIFO: It processes requests as they come. If there are too many processes, it deteriorates to “random”.However, it avoids starvation.
Shortest Seek Time First: Out of a list of requests, pick the ones that minimise seek time. Performance is excellent, but is susceptible to starvation.
Elevator (SCAN): Out of a list of requests, we move the head in one direction and back again. It services requests in track order until reaching the highest, then reverses. Performance is good, not quite as good as SSTF, but avoids starvation.
Modified Elevator (Circular-SCAN): Similar to elevator, but reads sectors in only one direction. It does not down-scan, instead electing to go back to the first track and start again. This gives it better locality on sequential reads and reduces maximum delay to read a particular sector.
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