UGC NET CSE | June 2023 | Part 2: 14

Question

 

Consider a disk system with cylinders. The request to access the cylinders occurs in the following sequence:
\[
4,34,10,7,19,73,2,15,6,20
\]
Assuming that the head is currently at cylinder $50$, what is the time taken to satisfy all requests if it takes $1 \mathrm{~ms}$ to move from one cylinder to adjacent one and shortest seek time first policy is used?

• A. $119 \mathrm{~ms}$
• B. $120 \mathrm{~ms}$
• C. $142 \mathrm{~ms}$
• D. $146 \mathrm{~ms}$

Answer 1

In shortest seek time first, the access request for cylinder closest to current position is served first.

Given, head is currently at cylinder 50, the sequence of requests served will be –
50 → 34 → 20 → 19 → 15 → 10 → 7 → 6 → 4 → 2 → 73

Total head movement = 119

Time for 1 move = 1ms

Total seek time = 119*1ms = 119ms