Question

Disk requests come into the disk driver for cylinders 10, 22, 20, 2, 40, 6, and 38, in that order. Assume that the disk has 100 cylinders numbered 0 through 99. The arm (head) is initially at cylinder 20. Based on the following disk scheduling algorithms, draw scheduling diagram indicating the movement of the head as arm (head) moves around the cylinders services the requests.

i. (5 points) First Come First Served

ii. (5 points) Shortest Seek Time First

iii. (5 points) SCAN

Answer 1

First come first serve (FCFS) In this algorithm, the requests are addressed in the they are in the queue. 10, 22, 20+2, 40, 6 head initially at: 20 Same order as 38 38 40 99 0 2 6 10 2022 1) Shortest Seek Time first (SSTF) In this algorithm, the requests which are nearest to the current head position are addressed forst. In other words, the request whose seek time is shortest is executed first. 38 40 99 0 26 10 20 22

in its path come in 1) SICAN In this algorithm, the disk head moves in a specific direchon and executes requests requests that in that direchon. And once it reaches the disk end (99 in this case), it reverses direction and executes the remaining requests. 99 0 26 10 20 22 38 40 > laitos