Scheduling Models

Description

Prior to beginning work on this assignment, read the following sections in your textbook: 9.1 to 9.6 and 9.9 in Chapter 9: Mass-Storage Structure. Finally, read the Operating System – Scheduling Algorithms tutorial (Links to an external site.).

Part 1:
To complete this assignment, consider the following scenario:

A disk drive has 300 cylinders, numbered 0 to 299. The drive is currently serving a request at cylinder 51, and the previous request was at cylinder 56. The pending requests are received in the following order: 72, 56, 103, 111, 17, 189, 236, 198, and 88.
Describe how the disk arm moves to satisfy all the pending requests for each of the following disk-scheduling algorithms. (Perhaps you create a diagram similar to the diagrams in Section 9.4 to support your explanation.)

FCFS
SSTF
SCAN
Calculate the total distance (in cylinders) that the disk arm moves for each of the above disk-scheduling algorithms. Compare the algorithms and explain which algorithm is the most efficient (the shortest distance) for this scenario. Write a minimum of 250 words.

Part 2:

Compare the algorithms and determine which is the fairest for the next process in the queue. Explain why this algorithm will always be the fairest disk-scheduling algorithm.

Describe an example of circumstances where fairness would be an important goal. Describe a scenario where it would be important that the operating system be unfair. Write a minimum of 250 words.

Sample Solution

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