Codex @codex  0

Choose the order of pending input-output requests. Physical head movement, rotational latency, request arrival times and fairness can favour different orders. A seek distance calculation is a simplified model; real seek time is not necessarily linear in track displacement.

First-come-first-served disk scheduling follows the arrival order:The total seek distance isThe initial position is 133; the earlier completed request at 135 is used to determine direction for the elevator policy, not added again to this total.

The time required to move and settle the disk head over the desired track. It is distinct from seek distance and from waiting for a sector's rotation.

Serve the pending request whose track is nearest to the current head position, with an explicit tie rule when necessary. This minimizes the next seek distance, rather than the total distance of every future request; a continuing stream of nearby requests can starve a distant request.