6 on a disk with 200 cylinders numbers 0 to 199 compute the...

6) On a disk with 200 cylinders, numbers 0 to 199, compute the number of tracks the disk arm must move to the satisfy the entire request in the disk queue. Assume the last request received was at track 100. The queue in FIFO order contains requests for the following tracks, 55, 58, 39, 18, 90, 160, 150, 38, 184. Perform the computation to find the seek length for the following scheduling algorithm. (i) FCFS (ii) SSTF (iii) SCAN (iv) C-SCAN (v) LOOK

Transcript

00:01 Hello student here the data is given disk with 200 cylinder number 0 to 199 and the last request received at the track 100 queue of the request in fifo order 55 58 39 80 90 160 150 38 180 queue of request so all of this is given to us so now i have to apply first fcfs first come first serve algorithm the disk in the disk and calculate the seek length of the fcfs so here we know the disk arm simply moves through the queue in the order the requests are received so first come first serves the order in which order they will come it will be served first so here according to this it is at the 100 track so 100 to 55 the arm will move and so after 100 to 55 45 will come so in the similar way 55 to 58 3 will come 58 to 39 so 19 will come 39 to 18 so these are the track in which the disk is moving so this will come and 18 to 90 90 to 160 160 to 150 150 to 38 38 to 184 so total i have written total seek length of fcfs 45 plus 3 plus 19 plus 21 plus 72 plus 70 plus 10 plus 112 plus 146 and if we add these value it will come 498 so total seek length in the fcfs case will be 498 now i have to apply the second algorithm which is shortest seek time first so first initially it's on 100 track so shortest if we calculate the shortest then 90 will come first after that after 90 then it goes to 58 so this will give us the shortest so in the similar way we will calculate up to 184 and total value will come in this way so total seek time i have written in ssfs shortest seek time first this will come 10 plus 32 plus 3 plus 16 plus 1 plus 20 plus 132 plus 10 plus 20 which is giving us 248 so there is a total seek time in sstf is less as compared to fcfs third one is scan in this scan the arm moves in one direction either towards higher or the lower track number and serves all the requests in that direction so here the arm moved in one direction first so here initially it's on 100 arm is on 100 100 track so 100 to 150 in one direction move to the end after this 150…

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