Which disk scheduling algorithm might lead to a "sweeping" effect where requests are serviced in a patterned manner across the disk?

Question

BlackTom AI · Accepted Answer

The question asks which disk scheduling algorithm might produce a sweeping effect, where requests are serviced in a patterned, broad motion across the disk.
Since the provided data lacks the list of answer options, I cannot compare each choice directly. However, the indicated correct answer is 'b. SCAN', which aligns with the well-known behavior of the SCAN (elevator) algorithm.
Why SCAN produces a sweeping effect: SCAN moves the disk head in one direction (e.g., from the innermost track toward the outer tracks) servicing all pending requests along the way, until it hits a end of the disk, then it reverses direction and services requests on the return path. This results in broad, sweeping passes across the disk rather than random, isolated jumps between requests, creating the characteristic sweep pattern.
How this differs from other common algorithms (to illuminate why a sweeping pattern is specific to SCAN):
- FCFS (First-Ccome, First-Served) would not create a deliberate sweeping pattern; it simply serves requests in arrival order, which can look scattered.
- SSTF (Shortest Seek Time First) tends to cluster around nearby requests and can cause localized movement rather than a pronounced sweeping across the entire disk.
- C-SCAN (Circular SCAN) also produces a sweeping effect but in a unidirectional, continuous sweep with a jump from the end back to the start, which is a more uniform cyclic pattern rather than the two-pass sweep of SCAN.
- LOOK and C-LOOK modify SCAN by turning before the end of the disk when no more requests exist at the current direction, which can reduce unnecessary travel but still preserve a sweeping character during active passes.
In summary, the distinctive sweeping behavior—long, directional passes across large portions of the disk as the head travels toward an end and then reverses—is most characteristic of the SCAN algorithm, which is why that option is identified as correct.

Which disk scheduling algorithm might lead to a "sweeping" effect where requests are serviced in a patterned manner across the disk?

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