LOOK algorithm

LOOK is a hard disk scheduling algorithm that decides the order in which pending read and write requests are served. It resembles the SCAN elevator algorithm in serving requests in both sweep directions, but it looks ahead for pending requests in the direction of travel and reverses as soon as none remain, so the arm goes only as far as the final request in each direction rather than to the edge of the disk. This avoids the starvation problem of shortest seek time first, though it is biased toward tracks clustered at the edges and toward more recent jobs. Variants include circular LOOK, which scans in one direction only, N-LOOK and F-LOOK, which split the queue into sub queues for fairness, and shortest LOOK. Average seek times are slightly better than SCAN.