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    Question

    Which of the following I/O scheduling algorithms

    provides the most efficient disk access for systems with many requests clustered around a central location on the disk? 
    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 LOOK algorithm is an optimized version of the SCAN algorithm. It moves the disk arm in one direction servicing requests, and when it reaches the end, it reverses direction, servicing requests in that direction. LOOK improves on SCAN by stopping the movement as soon as there are no requests in the current direction, thereby reducing unnecessary disk movement. This results in more efficient disk access, especially when requests are clustered near a central location. Option A (FCFS): FCFS is the simplest scheduling algorithm but not optimal for disk I/O since it can result in significant seek times as the disk arm moves back and forth across the disk. Option B (SSTF): While SSTF minimizes the seek time by always choosing the request closest to the current position, it can cause starvation for requests that are far from the current head position, and it's not ideal for clustered requests. Option C (SCAN): SCAN is less efficient than LOOK because it always scans to the end of the disk, even if there are no requests to be serviced in that direction. Option E (CLOOK): CLOOK is a variation of LOOK that moves in one direction and then jumps to the other side of the disk, but for clustered requests, LOOK is generally more efficient as it doesn’t require the disk to jump to the opposite end.

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