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Recent questions tagged disk-scheduling

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DRDO CSE 2022 Paper 2 | Question: 8
If the disk head is initially located at track $32,$ find the number of disk moves required with First Come First Serve $\text{(FCFS)}$ scheduling criteria if the disk queue of $\text{I/O}$ blocks requests are: $90 \; 77 \; 24 \; 104 \; 55 \; 87.$

admin asked in Operating System Dec 15, 2022

by admin

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Applied Test Series
A disk drive has 5000 cylinders, numbered 0 to 4999. The drive is serving a request at cylinder 143 currently and the previous request was at 125. The disk I/O queue, in FIFO order, is 86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130 ... the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests, for SCAN?

LRU asked in Operating System Dec 28, 2021

by LRU

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1 vote

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Live Test Series Live: Applied
We are given a hard disk of 500 GB. The performance details are : 5000 RPM rotation rate 200 cylinders, numbered from 1 to 200 Takes 1 + (n/20) milliseconds to move heads across n cylinders (e.g., from i to i + n). A ... the head travels half the cylinders and half a revolution. The average time taken to read a 1MB block from the hard disk is__? Need help.

ramakrushna asked in CO and Architecture Dec 22, 2021

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Applied Grand Test 2
Given a disk with 100 cylinders (0 to 99). Exactly one time unit is required to move the read/write head from one cylinder to the next. At time 0 the heads are at cylinder 0 and no requests are pending. The following six requests ... of the heads in movement. Assuming, that rotational and transfer times are negligible, the total time required for the Scan algorithm is _____

LRU asked in Operating System Nov 22, 2021

by LRU

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2 votes

2 answers

5

Applied Test Series
In a system SCAN, disk scheduling policy has been used. The number of tracks traversed by the head if the disk has 200 tracks and the requested tracks, in the order received, are 65, 48, 39, 08, 99, 164, 152, 38, 124 PS : Assume initial head position is at 65, and it will move towards 0

LRU asked in Operating System Oct 20, 2021

by LRU

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3 answers

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UGC NET CSE | October 2020 | Part 2 | Question: 16
Consider a disk system having $60$ cylinders. Disk requests are received by a disk drive for cylinders $10,22,20,2,40,6$ and $38$, in that order. Assuming the disk head is currently at cylinder $20$, what is the ... one and Shortest Seek Time First (SSTF) algorithm is used? $240$ milliseconds $96$ milliseconds $120$ milliseconds $112$ milliseconds

go_editor asked in Operating System Nov 20, 2020

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NIELIT 2017 OCT Scientific Assistant A (CS) - Section B: 35
Disk request come to a disk driver for cylinders in the order $10,22,20,2,40,6$ and $38,$ at a time when the disk drive is reading from cylinder $20$. The seek time is $6\text{ ms}$ per cylinder. The total seek time, if the disk arm scheduling algorithm is first-come-first-served is $900$ ms $850$ ms $360$ ms $876$ ms

Lakshman Patel RJIT asked in Operating System Apr 1, 2020

by Lakshman Patel RJIT

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NIELIT 2017 July Scientist B (CS) - Section B: 35
A disk has $200$ tracks (numbered $0$ through $199$). At a given time, it was servicing the request of reading data from track $120$, and at the previous request, service was for track $90$. The pending requests (in order of their arrival) are for track numbers. ... ) and FCFS (First Come First Serve)? $2$ and $3$ $3$ and $3$ $3$ and $4$ $4$ and $4$

Lakshman Patel RJIT asked in Operating System Mar 30, 2020

by Lakshman Patel RJIT

533 views

1 vote

6 answers

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UGC NET CSE | January 2017 | Part 3 | Question: 50
Consider a disk queue with I/O requests on the following cylinders in their arriving order: $6,10,12,54,97,73,128,15,44,110,34,45$. The disk head is assumed to be at cylinder $23$ and moving in the direction of decreasing number of ... in the disk is $150$. The disk head movement using SCAN -scheduling algorithm is: $172$ $173$ $227$ $228$

go_editor asked in Operating System Mar 24, 2020

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6 votes

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GATE CSE 2020 | Question: 35
Consider the following five disk five disk access requests of the form (request id, cylinder number) that are present in the disk scheduler queue at a given time. $(P, 155), (Q,85), (R,110),(S, 30), (T,115)$ Assume the head is positioned at ... ,but before $T$. The head reverses its direction of movement between servicing of $Q$ and $P$. $R$ is serviced before $P$.

Arjun asked in Operating System Feb 12, 2020

by Arjun

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Andrew S. Tanenbaum (OS) Edition 4 Exercise 5 Question 56 (Page No. 434)
Write a program to implement the three disk-arm scheduling algorithms. Write a driver program that generates a sequence of cylinder numbers $(0–999)$ at random, runs the three algorithms for this sequence and prints out the total distance (number of cylinders) the arm needs to traverse in the three algorithms.

Lakshman Patel RJIT asked in Operating System Oct 28, 2019

by Lakshman Patel RJIT

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Andrew S. Tanenbaum (OS) Edition 4 Exercise 5 Question 32 (Page No. 432)
A slight modification of the elevator algorithm for scheduling disk requests is to always scan in the same direction. In what respect is this modified algorithm better than the elevator algorithm?

Lakshman Patel RJIT asked in Operating System Oct 28, 2019

by Lakshman Patel RJIT

560 views

1 vote

1 answer

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Andrew S. Tanenbaum (OS) Edition 4 Exercise 5 Question 31 (Page No. 432)
Disk requests come in to the disk driver for cylinders $10, 22, 20, 2, 40, 6,$ and $38,$ in that order. A seek takes $6\: msec$ per cylinder. How much seek time is needed for First-come, first served. Closest cylinder next. Elevator algorithm (initially moving upward). In all cases, the arm is initially at cylinder 20.

Lakshman Patel RJIT asked in Operating System Oct 28, 2019

by Lakshman Patel RJIT

1.2k views

2 votes

5 answers

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UGC NET CSE | June 2019 | Part 2 | Question: 41
Consider a disk system with $100$ cylinders. The requests to access the cylinders occur in the following sequences: $4, 34, 10, 7, 19, 73, 2, 15, 6, 20$ Assuming that the head is currently at cylinder $50$, what is the time taken to ... the cylinder to adjacent one and the shortest seek time first policy is used? $357$ ms $238$ ms $276$ ms $119$ ms

Arjun asked in Operating System Jul 2, 2019

by Arjun

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Galvin Edition 9 Exercise 10 Question 15 (Page No. 499-500)
Compare the performance of $C-SCAN$ and $SCAN$ scheduling, assuming a uniform distribution of requests. Consider the average response time (the time between the arrival of a request and the completion of that request's ... and the effective bandwidth. How does performance depend on the relative sizes of seek time and rotational latency ?

akash.dinkar12 asked in Operating System Mar 22, 2019

by akash.dinkar12

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Galvin Edition 9 Exercise 10 Question 11 (Page No. 498-499)
Suppose that a disk drive has $5,000$ cylinders, numbered $0$ to $4,999$. The drive is currently serving a request at cylinder $2,150$, and the previous request was at cylinder $1,805$. The queue of pending requests, in $FIFO$ ... disk-scheduling algorithms ? $a. FCFS$ $b. SSTF$ $c. SCAN$ $d. LOOK$ $e. C-SCAN$ $f. C-LOOK$

akash.dinkar12 asked in Operating System Mar 22, 2019

by akash.dinkar12

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Galvin Edition 9 Exercise 10 Question 10 (Page No. 498)
Explain why $SSDs$(Solid State Drives) often use an $FCFS$ disk-scheduling algorithm.

akash.dinkar12 asked in Operating System Mar 22, 2019

by akash.dinkar12

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Galvin Edition 9 Exercise 10 Question 9 (Page No. 498)
None of the disk-scheduling disciplines, except $FCFS$, is truly fair (starvation may occur). a. Explain why this assertion is true. b. Describe a way to modify algorithms such as $SCAN$ to ensure fairness. c. Explain why ... more examples of circumstances in which it is important that the operating system be unfair in serving $I/O$ requests.

akash.dinkar12 asked in Operating System Mar 22, 2019

by akash.dinkar12

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