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Disk requests come to a disk driver for cylinders in the order 176, 79, 34, 60, 92, 11, 41 and 114. The initial head is positioned at 50 and the direction is moving from left to right. What is the total head movement (in the number of cylinders) incurred while servicing these requests, if LOOK scheduling is used?
Correct answer is '291'. Can you explain this answer?
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Disk requests come to a disk driver for cylinders in the order 176, 79...
Explanation:
The LOOK disk scheduling algorithm is a variant of the SCAN algorithm. It works by moving the disk arm only in the direction of the pending requests, instead of going all the way to the end of the disk.
Step 1: Sorting the Disk Requests
Before calculating the total head movement, we need to sort the disk requests in ascending order. The sorted order of the given disk requests is as follows:
11, 34, 41, 60, 79, 92, 114, 176
Step 2: Calculating the Total Head Movement
To calculate the total head movement, we need to determine the order in which the disk requests will be serviced.
1. Initially, the head is positioned at cylinder 50 and the direction is moving from left to right.
2. Starting from cylinder 50, we move towards the right until we find the first disk request greater than 50, which is 60. The head movement from 50 to 60 is 10 cylinders.
3. We continue moving towards the right and process the remaining disk requests in ascending order. The head movement from 60 to 79 is 19 cylinders, from 79 to 92 is 13 cylinders, and from 92 to 114 is 22 cylinders.
4. After servicing the request at cylinder 114, we change the direction of the head movement since there are no more requests towards the right.
5. We move towards the left and process the remaining disk requests in ascending order. The head movement from 114 to 92 is 22 cylinders, from 92 to 79 is 13 cylinders, from 79 to 60 is 19 cylinders, from 60 to 41 is 19 cylinders, from 41 to 34 is 7 cylinders, and from 34 to 11 is 23 cylinders.
6. Finally, after servicing the request at cylinder 11, we reach the end of the disk and the total head movement is calculated.
Calculating the Total Head Movement:
Head movement from 50 to 60 (right) = 10 cylinders
Head movement from 60 to 79 (right) = 19 cylinders
Head movement from 79 to 92 (right) = 13 cylinders
Head movement from 92 to 114 (right) = 22 cylinders
Head movement from 114 to 92 (left) = 22 cylinders
Head movement from 92 to 79 (left) = 13 cylinders
Head movement from 79 to 60 (left) = 19 cylinders
Head movement from 60 to 41 (left) = 19 cylinders
Head movement from 41 to 34 (left) = 7 cylinders
Head movement from 34 to 11 (left) = 23 cylinders
Total head movement = 10 + 19 + 13 + 22 + 22 + 13 + 19 + 19 + 7 + 23 = 177 cylinders
Therefore, the total head movement incurred while servicing these requests using the LOOK scheduling algorithm is 177 cylinders.
The LOOK disk scheduling algorithm is a variant of the SCAN algorithm. It works by moving the disk arm only in the direction of the pending requests, instead of going all the way to the end of the disk.
Step 1: Sorting the Disk Requests
Before calculating the total head movement, we need to sort the disk requests in ascending order. The sorted order of the given disk requests is as follows:
11, 34, 41, 60, 79, 92, 114, 176
Step 2: Calculating the Total Head Movement
To calculate the total head movement, we need to determine the order in which the disk requests will be serviced.
1. Initially, the head is positioned at cylinder 50 and the direction is moving from left to right.
2. Starting from cylinder 50, we move towards the right until we find the first disk request greater than 50, which is 60. The head movement from 50 to 60 is 10 cylinders.
3. We continue moving towards the right and process the remaining disk requests in ascending order. The head movement from 60 to 79 is 19 cylinders, from 79 to 92 is 13 cylinders, and from 92 to 114 is 22 cylinders.
4. After servicing the request at cylinder 114, we change the direction of the head movement since there are no more requests towards the right.
5. We move towards the left and process the remaining disk requests in ascending order. The head movement from 114 to 92 is 22 cylinders, from 92 to 79 is 13 cylinders, from 79 to 60 is 19 cylinders, from 60 to 41 is 19 cylinders, from 41 to 34 is 7 cylinders, and from 34 to 11 is 23 cylinders.
6. Finally, after servicing the request at cylinder 11, we reach the end of the disk and the total head movement is calculated.
Calculating the Total Head Movement:
Head movement from 50 to 60 (right) = 10 cylinders
Head movement from 60 to 79 (right) = 19 cylinders
Head movement from 79 to 92 (right) = 13 cylinders
Head movement from 92 to 114 (right) = 22 cylinders
Head movement from 114 to 92 (left) = 22 cylinders
Head movement from 92 to 79 (left) = 13 cylinders
Head movement from 79 to 60 (left) = 19 cylinders
Head movement from 60 to 41 (left) = 19 cylinders
Head movement from 41 to 34 (left) = 7 cylinders
Head movement from 34 to 11 (left) = 23 cylinders
Total head movement = 10 + 19 + 13 + 22 + 22 + 13 + 19 + 19 + 7 + 23 = 177 cylinders
Therefore, the total head movement incurred while servicing these requests using the LOOK scheduling algorithm is 177 cylinders.
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Community Answer
Disk requests come to a disk driver for cylinders in the order 176, 79...
The total head movement,
= (60 − 50) + (79 − 60) + (92 − 79) + (114 − 92) + (176 − 114) + (176 − 41) +( 41 − 34) + (34 − 11)
= 291
Hence, the correct answer is 291.
= (60 − 50) + (79 − 60) + (92 − 79) + (114 − 92) + (176 − 114) + (176 − 41) +( 41 − 34) + (34 − 11)
= 291
Hence, the correct answer is 291.
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Disk requests come to a disk driver for cylinders in the order 176, 79, 34, 60, 92, 11, 41 and 114. The initial head is positioned at 50 and the direction is moving from left to right. What is the total head movement (in the number of cylinders) incurred while servicing these requests, if LOOK scheduling is used?Correct answer is '291'. Can you explain this answer?
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Disk requests come to a disk driver for cylinders in the order 176, 79, 34, 60, 92, 11, 41 and 114. The initial head is positioned at 50 and the direction is moving from left to right. What is the total head movement (in the number of cylinders) incurred while servicing these requests, if LOOK scheduling is used?Correct answer is '291'. Can you explain this answer? for Computer Science Engineering (CSE) 2024 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 Disk requests come to a disk driver for cylinders in the order 176, 79, 34, 60, 92, 11, 41 and 114. The initial head is positioned at 50 and the direction is moving from left to right. What is the total head movement (in the number of cylinders) incurred while servicing these requests, if LOOK scheduling is used?Correct answer is '291'. Can you explain this answer? covers all topics & solutions for Computer Science Engineering (CSE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Disk requests come to a disk driver for cylinders in the order 176, 79, 34, 60, 92, 11, 41 and 114. The initial head is positioned at 50 and the direction is moving from left to right. What is the total head movement (in the number of cylinders) incurred while servicing these requests, if LOOK scheduling is used?Correct answer is '291'. Can you explain this answer?.
Disk requests come to a disk driver for cylinders in the order 176, 79, 34, 60, 92, 11, 41 and 114. The initial head is positioned at 50 and the direction is moving from left to right. What is the total head movement (in the number of cylinders) incurred while servicing these requests, if LOOK scheduling is used?Correct answer is '291'. Can you explain this answer? for Computer Science Engineering (CSE) 2024 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 Disk requests come to a disk driver for cylinders in the order 176, 79, 34, 60, 92, 11, 41 and 114. The initial head is positioned at 50 and the direction is moving from left to right. What is the total head movement (in the number of cylinders) incurred while servicing these requests, if LOOK scheduling is used?Correct answer is '291'. Can you explain this answer? covers all topics & solutions for Computer Science Engineering (CSE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Disk requests come to a disk driver for cylinders in the order 176, 79, 34, 60, 92, 11, 41 and 114. The initial head is positioned at 50 and the direction is moving from left to right. What is the total head movement (in the number of cylinders) incurred while servicing these requests, if LOOK scheduling is used?Correct answer is '291'. Can you explain this answer?.
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