An application loads 100 libraries at start-up. Loading each library requires…
2011
An application loads 100 libraries at start-up. Loading each library requires exactly one disk access. The seek time of the disk to a random location is given as 10 milliseconds. Rotational speed of disk is 6000 rpm. If all 100 libraries are loaded from random locations on the disk, how long does it take to load all libraries? (The time to transfer data from the disk block once the head has been positioned at the start of the block may be neglected)
Answer: B. 1.50 s — Key idea: each library load requires one seek plus an average rotational latency; transfer time is neglected. Rotation speed: 6000 rpm = 6000/60 = 100…
- A.
0.50 s
- B.
1.50 s
- C.
1.25 s
- D.
1.00 s
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Correct answer: B
Key idea: each library load requires one seek plus an average rotational latency; transfer time is neglected.
Rotation speed: 6000 rpm = 6000/60 = 100 rotations per second → period = 1/100 s = 0.01 s = 10 ms.
Average rotational latency = half a rotation = 10 ms / 2 = 5 ms.
Seek time = 10 ms.
Time per library access = seek time + average rotational latency = 10 ms + 5 ms = 15 ms.
Total for 100 libraries = 100 × 15 ms = 1500 ms = 1.5 s.
Answer: 1.5 s
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