Question

In: Operations Management

Suppose that a disk drive has 5,000 cylinders, numbered 0 to 4,999. The drive is currently...

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 order, is:

2,069, 1,212, 2,296, 2,800, 544, 1,618, 356, 1,523, 4,965, 3681

Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for each of the following disk-scheduling algorithms?

FCFS
SSTF
SCAN
LOOK
C-SCAN
C-LOOK

Expert Solution

Disk-scheduling algorithms is an approach used by operating system to plan the input and output request for accessing the disk. The purpose of it is to reduce the total seek time.The time required to read or write the disc block determined by three factors:

Seek time: Time to move the section to the proper cylinder
Rotational delay: The time for a proper part to rotate under the head
Actual time of data transfer

As per the Given data, the number of cylinders are 5000 which is numbered from 0 to 4999.

The current head position of cylinder is 2150.

The previous request of the cylinder was 1805 (to determine the direction in which the line is moving)

Queue in FIFO order is 2069, 1212, 2296, 2800, 544, 1618, 356, 1,523, 4,965, 3681

Now, let us calculate the total distance in the cylinders by following disk-scheduling algorithms.

a) FCFS

It stands for First come First serve. It is just like FIFO queue data structure. The data which is added in the queue first will also leaves the queue first. This method is used in batch systems. This is a simple scheduling algorithm as it performs according to the request order.

FCFS = (2150-2069)+(2069-1212)+(1212-2296)+(2296-2800)+(2800-544)+(544-1618)+

(1618-356)+(356-1523)+(1523-4965)+(4965-3681)

FCFS=

=

b) SSTF

It stands for shortest seek time first. It selects the disk input and output request which requires minimum seek time from its current position of head.

SSTF=

=

c) SCAN

This is also known as Elevator algorithm. Its head goes from one end to another and then it takes reverse direction.

SCAN

=

d) LOOK

It is an improved version of SCAN. Head starts from the first request at one end of the disk and then it moves to the last request fulfilling all the requests in between. After reaching last request it takes reverse direction.

e) C-SCAN

Its stands for circular SCAN which means it starts from head from end of the disk and moves towards the other end servicing all the requests comes in between. It the takes a reverse direction. It then returns to starting point without servicing any request which comes in between.

f) C-LOOK

It is a modified version of the LOOK algorithm. It scans all the cylinders from lowest to highest place. But the only difference is that head moves in only one direction.

We were unable to transcribe this image

keosha answered 1 year ago

Suppose that a disk drive has 6,000 cylinders, numbered 0 to 5999. The drive is currently...

Suppose that a disk drive has 6,000 cylinders, numbered 0 to 5999. The drive is currently serving a request at cylinder 3150, and the previous request was at cylinder 1805 (Hint: this indicates the reading head's moving direction). The queue of pending requests, in FIFO order, is: 3511, 2332, 2800, 3192, 658, 1296, 1918, 1356, 5936, 2527 Starting from the current head position, what is the total distance in cylinders) that the disk arm moves to satisfy all the pending requests for...

Suppose that a disk drive has 4,000 cylinders, numbered 0 to 3999. The drive is currently...

Suppose that a disk drive has 4,000 cylinders, numbered 0 to 3999. The drive is currently serving a request at cylinder 2250, and the previous request was at cylinder 1205. The queue of pending requests, in FIFO order is: 1870, 2150, 1250, 778, 3598 Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for each of the following disk-scheduling algorithms? (show your working steps) FCFS...

1. A hard disk drive has 16 platters, 8192 cylinders, and 256 4KB sectors per track....

1. A hard disk drive has 16 platters, 8192 cylinders, and 256 4KB sectors per track. The storage capacity of this disk drive is at most Select one: a. 32 GB. b. 128 GB. c. 32 TB. 2. To further optimize I/O performance, some SSD schedulers Select one: a. merge adjacent write requests but not adjacent read requests. b. do not merge requests at all. c. merge adjacent read requests but not adjacent write requests. 3. What steps are necessary...

Question 1: On a disk with 1000 cylinders, number 0 to 999, compute the number of...

Question 1: On a disk with 1000 cylinders, number 0 to 999, compute the number of tracks the disk arm must move to satisfy all the requests in the disk queue. Assume the last request serviced was at track 345 and the head is moving toward track 0. The queue in FIFO order contains requests for the following tracks: 123, 847, 692, 475, 105, 376. Perform the computations for the following disk scheduling algorithms: a) FCFS b) SSTF...

A fair four sided die has two faes numbered 0 and two faces numbered 2. Another...

A fair four sided die has two faes numbered 0 and two faces numbered 2. Another fair four sided die has its faces numbered 0,1,4, and 5. The two dice are rolled. Let X and Y be the respective outcomes of the roll. Let W = X + Y. (a) Determine the pmf of W. (b) Draw a probability histogram of the pmf of W

A roulette wheel has 38 slots, numbered 0, 00, and 1 to 36. The slots 0...

A roulette wheel has 38 slots, numbered 0, 00, and 1 to 36. The slots 0 and 00 are colored green, 18 of the others are red, and 18 are black.The dealer spins the wheel and at the same time rolls a small ball along the wheel in the opposite direction. The wheel is carefully balanced so that the ball is equally likely to land in any slot when the wheel slows. Gamblers can bet on various combinations of numbers...

What is a traditional Hard Disk Drive (HDD) composed?

A computer disk drive is turned on starting from rest and has constant angular acceleration. Part...

A computer disk drive is turned on starting from rest and has constant angular acceleration. Part A If it took 0.420 s for the drive to make its second complete revolution, how long did it take to make the first complete revolution? Part B What is its angular acceleration, in rad/s2?

A box contains 4 tickets. 1 ticket is numbered 0, 1 ticket is numbered 1, and...

A box contains 4 tickets. 1 ticket is numbered 0, 1 ticket is numbered 1, and 2 tickets are numbered 2. Suppose n draws with replacement are made from this box. Let Sn be the sum of the numbers drawn. a) Approximate the probability P(S100=100)

Consider a hard disk drive that has 5 double-sided platters, each surface has 1000 tracks, each...

Consider a hard disk drive that has 5 double-sided platters, each surface has 1000 tracks, each track has 256 sectors of size 512 bytes. Each block (disk page) comprises of 8 sectors. The seek time between adjacent tracks in 1ms and the average seek time between two random tracks is 25ms. The disk rotates at a speed of 7200 rpm (revolutions per minute). Let’s say, we have a file of size 1 MB and it contains 2048 equal-sized records. 1....