[Solved] Which of the following statements best explains why SSTF can lead to starvation, and why SCAN or C-SCAN are preferred in heavy-load scenarios? | Operating Systems

Operating Systems - Disk Scheduling - SSTF, SCAN, C-SCAN

Which of the following statements best explains why SSTF can lead to starvation, and why SCAN or C-SCAN are preferred in heavy-load scenarios?

ASSTF picks the closest request, potentially ignoring far requests indefinitely; SCAN and C-SCAN guarantee servicing all requests by sweeping the disk head across all tracks.

BSSTF always services requests in arrival order, causing long waits for distant requests; SCAN and C-SCAN service requests in a fixed direction to prevent this.

CSSTF has higher overhead due to sorting requests; SCAN and C-SCAN have lower overhead and thus better performance under load.

DSSTF requires knowledge of all requests upfront; SCAN and C-SCAN can operate with partial knowledge, making them more scalable.

Step-by-Step Solution

Step 1: Understand SSTF starvation
SSTF always picks the nearest request, so requests far from the current head position may wait indefinitely.
Step 2: SCAN and C-SCAN fairness
They move the head in a fixed direction, servicing all requests in order, ensuring no starvation.
Step 3: Evaluate other options
Options B, C, and D contain incorrect claims: SSTF does not service requests in arrival order; it does not have higher overhead due to sorting; and it requires knowledge of all requests upfront similarly to SCAN and C-SCAN.
Final Answer:
Option A -> Option A
Quick Check:
SSTF picks the closest request, potentially ignoring far requests indefinitely; SCAN and C-SCAN guarantee servicing all requests by sweeping the disk head across all tracks. correctly explains starvation and fairness trade-offs.

Quick Trick: SSTF starves distant requests; SCAN/C-SCAN sweep all tracks fairly

Common Mistakes:

MISTAKES

Confusing SSTF with FCFS regarding request order
Assuming SSTF has higher computational overhead
Believing SCAN/C-SCAN require less request knowledge

Trap Explanation:

PITFALL

Option B incorrectly states SSTF services requests in arrival order; Option C misattributes overhead; Option D misrepresents knowledge requirements, tempting candidates who conflate algorithm complexity with scheduling fairness.

Interviewer Note:

CONTEXT

Tests understanding of starvation causes and why elevator algorithms are preferred under heavy load.

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Which of the following statements best explains why SSTF can lead to starvation, and why SCAN or C-SCAN are preferred in heavy-load scenarios?

Step 1: Understand SSTF starvation

Step 2: SCAN and C-SCAN fairness

Step 3: Evaluate other options

Final Answer:

Quick Check:

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