UGC NET CSE | October 2020 | Part 2 | Question: 16

Question

Consider a disk system having $60$ cylinders. Disk requests are received by a disk drive for cylinders $10,22,20,2,40,6$ and $38$, in that order. Assuming the disk head is currently at cylinder $20$, what is the time taken to satisfy all the requests if it takes $2$ milliseconds to move from one cylinder to adjacent one and Shortest Seek Time First (SSTF) algorithm is used?

• A. $240$ milliseconds
• B. $96$ milliseconds
• C. $120$ milliseconds
• D. $112$ milliseconds

Answer 1

Disk requests with head at 20

2  6 10  20  22  38  40

20--->22---->10--->6---->2------>38------>40 total head movements (2+12+4+4+36+2) =60

 

time= 60x2= 120ms option 3 is the ans

Answer 2

Head movement : 20_ 22_ 10_ 6_ 2_38_ 40 Toatal head mivements : ( 2+12+4+4+36+2 =60) 1 cylinder take 2 ms Then 60 cylinders take 60*2=120ms.

Hence option C is correct✅

Answer 3

Useing seek time first we will find the answer