GATE CS 2008 Q32 — I/O Scheduling

Seek latency (or seek time) is the time required for the disk read/write head to move from its current track to the target track.

The movement of the physical disk arm involves three main phases:

1. Acceleration: Overcoming the starting inertia of the arm to speed it up.
2. Constant Speed: Coasting at maximum velocity (only for longer seek distances).
3. Deceleration and Settling: Overcoming the stopping inertia to slow down and precisely align the head over the target track.

Because of the starting and stopping inertia of the mechanical arm, a significant portion of the seek time is spent accelerating and decelerating, especially for short distances. Consequently, the seek time does not scale linearly with the number of tracks crossed.

Why other options are incorrect:

• Option A: The distribution of requests affects the overall queueing delay and average seek time of a workload, but it does not alter the physical seek latency characteristic of the drive itself.
• Option C: The higher capacity of outer tracks (due to zone bit recording) affects data transfer rates, not the mechanical movement of the arm.
• Option D: Disk scheduling policies (like SSTF, SCAN) determine the order of requests to minimize total seek time, but they do not change the physical relationship between seek distance and seek latency.