All Courses
Explore Courses UPSC Exam UPSC Test Series Free Notes EduRev Infinity Get the App Login Join for Free
Sign in Open App
Computer Science Engineering (CSE) Exam  >  Computer Science Engineering (CSE) Questions  >  Disk requests are received by a disk drive fo... Start Learning for Free
Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet served
  • a)
    125 msec
  • b)
    295 msec
  • c)
    575 msec
  • d)
    750 msec
Correct answer is option 'B'. Can you explain this answer?
Clear all your Computer Science Engineering (CSE) doubts with EduRev
Most Upvoted Answer
Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, ...
Shortest Seek First (SSF) Algorithm

The Shortest Seek First (SSF) algorithm aims to minimize the seek time by serving the disk requests in the order of their closest proximity to the current position of the disk arm.

Given Information:
- Disk requests: 5, 25, 18, 3, 39, 8, 35
- Initial position of the disk arm: 20
- Seek time per cylinder moved: 5 msec

Calculating Seek Time for SSF Algorithm:

1. Calculate the seek time for each request based on the SSF algorithm:
- Calculate the absolute difference between the current position of the disk arm and each request.
- Sort the requests in ascending order of their absolute differences.

Sorted requests based on absolute differences:
18, 25, 8, 35, 5, 39, 3

2. Calculate the seek time for each request by multiplying its absolute difference by the seek time per cylinder moved:
- Seek time for request 18: 5 * (18 - 20) = -10 msec (Negative value indicates movement in the opposite direction)
- Seek time for request 25: 5 * (25 - 20) = 25 msec
- Seek time for request 8: 5 * (8 - 20) = -60 msec
- Seek time for request 35: 5 * (35 - 20) = 75 msec
- Seek time for request 5: 5 * (5 - 20) = -75 msec
- Seek time for request 39: 5 * (39 - 20) = 95 msec
- Seek time for request 3: 5 * (3 - 20) = -85 msec

3. Calculate the total seek time by summing up the seek times of all requests:
Total Seek Time = -10 + 25 - 60 + 75 - 75 + 95 - 85 = -25 msec

Explanation:
The negative and positive seek times indicate the direction in which the disk arm needs to move. A negative value means it needs to move towards lower cylinder numbers, while a positive value means it needs to move towards higher cylinder numbers.

In this case, the total seek time is -25 msec, indicating that the disk arm needs to move towards lower cylinder numbers. The absolute value of the seek time (-25) represents the total distance the disk arm needs to travel in terms of cylinders.

Final Answer:
Therefore, the seek time needed to serve the given requests using the Shortest Seek First (SSF) algorithm is 25 msec. Hence, option B is the correct answer.
Free Test
FREE
Start Free Test
Start Free Test
Community Answer
Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, ...
The arm is at cylinder 20, so the service order = 18, 25, 35, 39, 8, 5, 3. Seek time = (20−18) + (25−18) + (35−25) + (39−35) + (39−8) + (8−5) + (5−3) = 2 + 7 + 10 + 4 + 31 + 3 + 2 = 59 Total seek time = 59 * 5 = 295 Option (B) is correct.
Explore Courses for Computer Science Engineering (CSE) exam

Similar Computer Science Engineering (CSE) Doubts

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.

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?

Top Courses for Computer Science Engineering (CSE)View all

Top Courses for Computer Science Engineering (CSE)

Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. Can you explain this answer?
Question Description
Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. 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 Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. 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 Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. Can you explain this answer?.
Solutions for Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. 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.
Here you can find the meaning of Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. Can you explain this answer? defined & explained in the simplest way possible. Besides giving the explanation of Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. Can you explain this answer?, a detailed solution for Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. Can you explain this answer? has been provided alongside types of Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. Can you explain this answer? theory, EduRev gives you an ample number of questions to practice Disk requests are received by a disk drive for cylinder 5, 25, 18, 3, 39, 8 and 35 in that order. A seek takes 5 msec per cylinder moved. How much seek time is needed to serve these requests for a Shortest Seek First (SSF) algorithm? Assume that the arm is at cylinder 20 when the last of these requests is made with none of the requests yet serveda)125 msecb)295 msecc)575 msecd)750 msecCorrect answer is option 'B'. Can you explain this answer? tests, examples and also practice Computer Science Engineering (CSE) tests.
Explore Courses for Computer Science Engineering (CSE) exam

Top Courses for Computer Science Engineering (CSE)

Explore Courses
SaveJoin the Discussion on the App for FREE
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Get App
© EduRev
Education Revolution
Signup to see your scores go up within 7 days!
Access 1000+ FREE Docs, Videos and Tests
Takes less than 10 seconds to signup