Suppose that the head of a moving-head disk with 100 tracks,...

Suppose that the head of a moving-head disk with 100 tracks, numbered 0 to 99, is currently serving a request at track 40 and moving upwards. The queue of requests is kept in a FIFO queu as the following. 80, 30, 55, 20, 10, 90 Calculate the total number of head movements (in terms of tracks traversed) needed to satisfy these requests for the following disk-scheduling algorithms. Illustrate the head movement either graphically or other means. (i) FCFS scheduling (ii) SCAN scheduling (iii) SSTF scheduling

Transcript

00:01 Hello students, the total number of head movements for each of the given disc scheduling algorithm.

00:06 So, for the all the calculation we assume that the head starts at the 14th track.

00:13 So, and initially moving upwards.

00:16 So, the given queue as the given queue request is of 20, 80, 30, 55, 20, 10 and 90.

00:32 So, the total number of the track total number of tracks are 100 and the initial head point is 40.

00:47 Initial head point head position is are 40.

00:56 So, now we need to first see for the fcfs scheduling that is the first come first serve scheduling.

01:07 So, we are here and this the head moves to each request track in the order they are in a queue.

01:14 So, as you can see we will order them as 40 it is initially starting from the 40 then 80 then continuing our the queue given queue 40, 80, 30, 55, 20, 10.

01:35 So, now it moves to the next that is to the 80 with the 40 tracks with the 40 tracks and now this 80 will move to the 30 that is the next term with the 50 tracks with the 50 tracks.

01:55 The next is from 30 to 55 that will be 25 tracks, 25 tracks and now 55 to 20 that will be as 35 tracks and 20 to 10.

02:14 So, that is 10 tracks, 10 tracks and the last is from 10 to the last term is 90 that is the 90 that will be as for the 80 tracks, 80 tracks.

02:28 Fine now the total head movement total head movement are we just need to sum up of all this track 40 plus 50 plus 25 plus 35 plus 10 plus 80.

02:56 So, as that will be as the total will be the 240 tracks, 240 tracks.

03:06 Now, similarly now we will go for the second one that is as second is the scan scheduling, scan scheduling.

03:21 Well in the scan scheduling the head moves in the one direction that is in the upward in this case...

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