Which disk I/O scheduling algorithm minimizes head movement on spinning disks by sweeping from one end to the other?

• A. FCFS
• B. LOOK
• C. ROUND-ROBIN
• D. SCAN

Answer: (D)

The concept being tested is how the SCAN disk scheduling algorithm works. SCAN makes the disk head move in one direction across the disk, servicing every request it encounters, until it reaches the end of the disk, then it reverses and sweeps back the other way. This sweeping behavior keeps head movement orderly and predictable, reducing random seeks and the back-and-forth motion that can happen with other schemes.

This approach minimizes total head movement on spinning disks compared to first-come, first-served (which can bounce the head around based on arrival order) and is distinct from ROUND-ROBIN (which isn’t a typical disk-scheduling strategy at all). LOOK is similar to SCAN but stops at the furthest request in a direction rather than going all the way to the physical end; the question’s description of sweeping from end to end points to SCAN, not LOOK, as the best fit.