ITPEC FE Morning April 2022 Question 12
ITPEC FE Morning April 2022 — Question 12 of 80
Magnetic Disk Access Time — calculate approximate average access time from disk specs.
Given: average seek time 7.5 ms, track-to-track seek time 1.2 ms, rotational speed 7,200 rpm.
Step-by-step:
- Full rotation time = 60,000 ms / 7,200 = 8.33 ms
- Average rotational delay = 8.33 / 2 = 4.17 ms
- Access time = 7.5 + 1.2 + 4.17 = 12.87 ms
Answer: (b) 12.87
Why not others:
- (a) 11.67 — omits track-to-track seek time
- (c) 15.83 — uses full rotation instead of half
- (d) 25 — incorrect calculation
Key rule: Average rotational delay is always half of the full rotation time, since on average the read head waits for half a revolution to reach the target sector.
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