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What is the primary goal of the SCAN disk scheduling algorithm?

easy🧠 Conceptual Q1 of Q15
LLD - Design — Elevator System
What is the primary goal of the SCAN disk scheduling algorithm?
ATo randomly select requests to service next
BTo reduce the total seek time by moving the head in one direction servicing all requests
CTo service requests in the order they arrive without reordering
DTo always service the closest request regardless of direction
Step-by-Step Solution
Solution:

  1. Step 1: Understand SCAN algorithm behavior

    SCAN moves the disk head in one direction, servicing all requests until it reaches the end.

  2. Step 2: Identify the goal of SCAN

    This approach reduces seek time by minimizing back-and-forth movement.

  3. Final Answer:

    To reduce the total seek time by moving the head in one direction servicing all requests -> Option B

  4. Quick Check:

    SCAN goal = reduce seek time by directional scan [OK]
Quick Trick: SCAN moves head in one direction servicing all requests [OK]
Common Mistakes:
MISTAKES
  • Thinking SCAN services requests randomly
  • Confusing SCAN with FCFS (first-come, first-served)
  • Assuming SCAN always services closest request first

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