Disk scheduling strategies: Which disk scheduling algorithm moves the disk arm back and forth (like an elevator) to service all requests in its path?

Introduction / Context:
Disk scheduling algorithms aim to reduce seek time and improve throughput. Understanding their mechanics helps predict performance under different workloads and prevents pathological delays for requests at far tracks.

Given Data / Assumptions:

• Rotational latency is ignored; focus is on head movement (seek time).
• Multiple outstanding requests are queued.
• We compare common policies: FCFS, SSTF, SCAN.

Concept / Approach:
The SCAN algorithm, also known as the “elevator algorithm,” sweeps the disk arm in one direction, servicing requests along the path, then reverses direction and repeats. This provides better fairness than SSTF (which can starve distant requests) and better average seek time than FCFS under load.

Step-by-Step Solution:

Verification / Alternative check:
Compare with LOOK/C-SCAN variants: LOOK turns where the last request in that direction exists; C-SCAN moves in one direction and returns quickly to the beginning without servicing on the way back.

Why Other Options Are Wrong:
FCFS/FIFO: no directed arm sweep. SSTF: greedy nearest-seek choice, not guaranteed back-and-forth sweeping. “None of the above”: incorrect because SCAN matches perfectly.

Common Pitfalls:
Confusing SCAN with C-SCAN/LOOK; assuming SSTF equals SCAN under certain loads (they can coincide but are distinct algorithms).

Final Answer:
Scan