Using the SCAN disk scheduling algorithm, if the disk head starts at position 60 and the requests are at [15, 25, 55, 75, 85], what is the order of servicing requests when the head moves towards the highest track number first?

medium📝 Analysis Q4 of 15

LLD - Design — Elevator System

A[60, 75, 85, 55, 25, 15]

B[60, 55, 25, 15, 75, 85]

C[60, 75, 85, 15, 25, 55]

D[60, 85, 75, 55, 25, 15]

Step-by-Step Solution

Solution:

Step 1: Identify head direction and requests
The head starts at 60 and moves towards the highest track number first.
Step 2: Service requests in ascending order from 60 upwards
Requests greater than or equal to 60 are 75 and 85, serviced in order: 75, then 85.
Step 3: Reverse direction and service remaining requests
After reaching the highest request (85), the head reverses and services requests less than 60 in descending order: 55, 25, 15.
Final Answer:
[60, 75, 85, 55, 25, 15] -> Option A
Quick Check:
Head moves up first, then down servicing requests accordingly [OK]

Quick Trick: Service requests in head direction first, then reverse [OK]

Common Mistakes:

MISTAKES

Servicing requests in ascending order regardless of head direction
Not reversing direction after reaching the end
Skipping requests on the return path

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Using the SCAN disk scheduling algorithm, if the disk head starts at position 60 and the requests are at [15, 25, 55, 75, 85], what is the order of servicing requests when the head moves towards the highest track number first?

Step 1: Identify head direction and requests

Step 2: Service requests in ascending order from 60 upwards

Step 3: Reverse direction and service remaining requests

Final Answer:

Quick Check:

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