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    Question

    Which I/O scheduling algorithm prevents starvation of

    requests?
    A FCFS Correct Answer Incorrect Answer
    B SSTF Correct Answer Incorrect Answer
    C SCAN Correct Answer Incorrect Answer
    D LOOK Correct Answer Incorrect Answer
    E CLOOK Correct Answer Incorrect Answer

    Solution

    The SCAN scheduling algorithm, also called the Elevator Algorithm , prevents starvation by servicing requests in one direction until it reaches the end, then reversing direction. This ensures that every request, regardless of its position, gets serviced within a predictable timeframe.

    1. How SCAN Works: Requests are arranged based on their positions. The disk arm moves in a single direction, servicing requests, and reverses once it reaches the last request in that direction.
    2. Prevents Starvation: Since SCAN covers all requests in its path, even those far from the initial direction of the disk arm are eventually served.
    Example:
    • Requests: 98, 183, 37, 122, 14, 124, 65, 67 (Initial Head: 53)
    • SCAN Movement: 53 → 37 → 14 → Reverse → 65 → 67 → 98 → 122 → 124 → 183
    • This ensures fairness in servicing requests.
    Why Other Options Are Incorrect 1.    FCFS:
      • While fair, FCFS can lead to high seek times due to requests being served in the order of arrival without considering their proximity.
    2.    SSTF:
      • SSTF selects the closest request but may cause starvation for distant requests.
    3.    LOOK:
      • LOOK is similar to SCAN but does not traverse to the end of the disk; however, it also prevents starvation.
    4.    CLOOK:
      • CLOOK further optimizes LOOK but may still involve longer wait times for requests on the other side of the disk.

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