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A hard disk system has the following parameters:

  • Rotation speed – $6000$ rpm.
  • Size of each sector – $1$ KB.
  • Average number of sectors per track – $128$.

Based on these parameters, which of the following statements is/are CORRECT? 

  1. The average latency of the drive is less than $6$ milliseconds.
  2. The burst data rate of the drive is more than $10$ MB/sec.
  3. The average capacity per track is larger than $1$ MB.
  1. I only
  2. I and III only
  3. I and II only
  4. I, II, and III
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1 Answer

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Best answer
1. Average rotational latency in hard drive is

(1 / (RPM / 60)) * 0.5 * 1000  ms

Or, (30000 / RPM)  ms = 30000 / 6000 = 5 ms , this makes statement I correct .

2. The burst data rate is  average track capacity * rotations per second = 128 * 0.001 * 100 MB/sec = 12.5 MB per second ( as 1 KB = 0.001 MB ) , this makes statement II correct.

3. The average capacity of each track is average number of sectors per track *  the size per sector = (128 * 1) KB =128 KB, which makes statement III false .

So, only statement I and II are correct , which is option C .

4 Comments

I too not agreed with this,

Average seek time = 2 * average latency  

how this happens??
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Answer:

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