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A disk drive has 200 cylinders, numbered 0 to 199. Disk requests come to the disk driver for cylinders 82, 170, 43, 140, 24, 16 and 190. The driver is currently serving a request at a cylinder 50. How much seek time is needed for the FCFS algorithm?
    Correct answer is '642'. Can you explain this answer?
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    Most Upvoted Answer
    A disk drive has 200 cylinders, numbered 0 to 199. Disk requests come ...
    Seek Time Calculation for FCFS Algorithm

    To calculate the seek time for the FCFS (First-Come, First-Served) algorithm, we need to consider the order in which the disk requests are processed. The seek time is the total amount of time required for the disk arm to move from one cylinder to another.

    Given data:
    - Disk drive has 200 cylinders numbered from 0 to 199.
    - Disk requests: 82, 170, 43, 140, 24, 16, and 190.
    - Current cylinder: 50.

    Step 1: Calculate the distance between each consecutive cylinder request
    To calculate the seek time, we need to calculate the distance between each consecutive cylinder request. The distance is the absolute difference between two cylinder numbers.

    Distance between 50 and 82 = |82 - 50| = 32
    Distance between 82 and 170 = |170 - 82| = 88
    Distance between 170 and 43 = |43 - 170| = 127
    Distance between 43 and 140 = |140 - 43| = 97
    Distance between 140 and 24 = |24 - 140| = 116
    Distance between 24 and 16 = |16 - 24| = 8
    Distance between 16 and 190 = |190 - 16| = 174

    Step 2: Calculate the total seek time
    The total seek time is the sum of the distances calculated in step 1.

    Total seek time = 32 + 88 + 127 + 97 + 116 + 8 + 174 = 642

    Therefore, the correct answer is 642, which represents the total seek time required for the FCFS algorithm to process all the given disk requests starting from cylinder 50.
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    Community Answer
    A disk drive has 200 cylinders, numbered 0 to 199. Disk requests come ...
    FCFS is the simplest disk scheduling algorithm. As the name suggests, this algorithm entertains requests in the order they arrive in the disk queue. The algorithm looks very fair and there is no starvation (all requests are serviced sequentially) but generally, it does not provide the fastest service.
    Algorithm:
    1. Let Request array represents an array storing indexes of tracks that have been requested in ascending order of their time of arrival. ‘head’ is the position of disk head.
    2. Let us one by one take the tracks in default order and calculate the absolute distance of the track from the head.
    3. Increment the total seek count with this distance.
    4. Currently serviced track position now becomes the new head position.
    5. Go to step 2 until all tracks in the request array have not been serviced.
    Given,
    A disk drive has cylinders = 200
    They are numbered 0 to 199.
    Disk requests come to the disk driver for cylinders 82, 170, 43, 140, 24, 16 and 190.
    The driver is currently serving a request at a cylinder 50.
    So, total seek time:
    = (82 − 50) + (170 − 82) + (170 − 43) + (140 − 43) + (140 − 24) + (24 − 16) + (190 − 16)
    = 642
    Hence, the correct answer is 642.
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    Consider a storage disk with 4 platters (numbered as 0, 1, 2 and 3), 200 cylinders (numbered as 0, 1, … , 199), and 256 sectors per track (numbered as 0, 1, … , 255). The following 6 disk requests of the form [sector number, cylinder number, platter number] are received by the disk controller at the same time: [120, 72, 2] , [180, 134, 1] , [60, 20, 0] , [212, 86, 3] , [56, 116, 2] , [118, 16, 1] Currently the head is positioned at sector number 100 of cylinder 80, and is moving towards higher cylinder numbers. The average power dissipation in moving the head over 100 cylinders is 20 milliwatts and for reversing the direction of the head movement once is 15 milliwatts. Power dissipation associated with rotational latency and switching of head between different platters is negligible. The total power consumption in milliwatts to satisfy all of the above disk requests using the Shortest Seek Time First disk scheduling algorithm is _______. Correct answer is '85'. Can you explain this answer?

    Consider a storage disk with 4 platters (numbered as 0, 1, 2 and 3), 200 cylinders (numbered as 0, 1, … , 199), and 256 sectors per track (numbered as 0, 1, … 255). The following 6 disk requests of the form [sector number, cylinder number, platter number] are received by the disk controller at the same time: [120, 72, 2], [180, 134, 1], [60, 20, 0], [212, 86, 3], [56, 116, 2], [118, 16, 1] Currently head is positioned at sector number 100 of cylinder 80, and is moving towards higher cylinder numbers. The average power dissipation in moving the head over 100 cylinders is 20 milliwatts and for reversing the direction of the head movement once is 15 milliwatts. Power dissipation associated with rotational latency and switching of head between different platters is negligible. The total power consumption in milliwatts to satisfy all of the above disk requests using the Shortest Seek Time First disk scheduling algorithm is ______ .Note -This was Numerical Type question.

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    A disk drive has 200 cylinders, numbered 0 to 199. Disk requests come to the disk driver for cylinders 82, 170, 43, 140, 24, 16 and 190. The driver is currently serving a request at a cylinder 50. How much seek time is needed for the FCFS algorithm?Correct answer is '642'. Can you explain this answer?
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    A disk drive has 200 cylinders, numbered 0 to 199. Disk requests come to the disk driver for cylinders 82, 170, 43, 140, 24, 16 and 190. The driver is currently serving a request at a cylinder 50. How much seek time is needed for the FCFS algorithm?Correct answer is '642'. Can you explain this answer? for Computer Science Engineering (CSE) 2025 is part of Computer Science Engineering (CSE) preparation. The Question and answers have been prepared according to the Computer Science Engineering (CSE) exam syllabus. Information about A disk drive has 200 cylinders, numbered 0 to 199. Disk requests come to the disk driver for cylinders 82, 170, 43, 140, 24, 16 and 190. The driver is currently serving a request at a cylinder 50. How much seek time is needed for the FCFS algorithm?Correct answer is '642'. Can you explain this answer? covers all topics & solutions for Computer Science Engineering (CSE) 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A disk drive has 200 cylinders, numbered 0 to 199. Disk requests come to the disk driver for cylinders 82, 170, 43, 140, 24, 16 and 190. The driver is currently serving a request at a cylinder 50. How much seek time is needed for the FCFS algorithm?Correct answer is '642'. Can you explain this answer?.
    Solutions for A disk drive has 200 cylinders, numbered 0 to 199. Disk requests come to the disk driver for cylinders 82, 170, 43, 140, 24, 16 and 190. The driver is currently serving a request at a cylinder 50. How much seek time is needed for the FCFS algorithm?Correct answer is '642'. Can you explain this answer? in English & in Hindi are available as part of our courses for Computer Science Engineering (CSE). Download more important topics, notes, lectures and mock test series for Computer Science Engineering (CSE) Exam by signing up for free.
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