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What is the main difference between the SCAN and LOOK disk scheduling algorithms?

easy🧠 Conceptual Q11 of Q15
LLD - Design — Elevator System
What is the main difference between the SCAN and LOOK disk scheduling algorithms?
ASCAN stops at the last request in the direction, LOOK goes to the disk edge
BLOOK moves the head randomly, SCAN moves sequentially
CLOOK stops at the last request in the direction, SCAN goes to the disk edge
DSCAN only moves in one direction, LOOK moves back and forth
Step-by-Step Solution
Solution:

  1. Step 1: Understand SCAN behavior

    SCAN moves the disk head to the end of the disk in one direction, servicing requests along the way.

  2. Step 2: Understand LOOK behavior

    LOOK moves the disk head only as far as the last request in the current direction, then reverses.

  3. Final Answer:

    LOOK stops at the last request in the direction, SCAN goes to the disk edge -> Option C

  4. Quick Check:

    LOOK stops early, SCAN goes to edge [OK]
Quick Trick: LOOK stops at last request, SCAN goes to disk edge [OK]
Common Mistakes:
MISTAKES
  • Confusing which algorithm stops at disk edge
  • Thinking LOOK moves randomly
  • Assuming SCAN moves only one way

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