GATE IT 2007 | Question: 44, ISRO2015-34

Question

A hard disk system has the following parameters :

• Number of tracks $= 500$
• Number of sectors/track $= 100$
• Number of bytes /sector $= 500$
• Time taken by the head to move from one track to adjacent track $= 1 \ ms$
• Rotation speed $= 600 \ rpm$.

What is the average time taken for transferring $250$ bytes from the disk ?

• A. $300.5 \ ms$
• B. $255.5 \ ms$
• C. $255 \ ms$
• D. $300 \ ms$

Comments

Average seek time = (Best case seek time + Worst case seek time) /  2

=> 0 + 499 /  2

=>249.5

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@Arjun sir @pC @VS what should we take avg seek time t/3 ? Or which is mentioned in the selected answer? if it comes this year again.

please clarify this.

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@Arjun sir Please tell us Which one should we consider for finding the Avg Seek Time

Worst Case Seek Time / 3

or

(Best Case Seek Time + Worst Case Seek time)/2

?

Answer 1

Average tracks in between a seek = $\frac{n+1}{3}$. In this case answer will be 217.5msec, but the solution doesn’t exist in the options.

The “best answer” provided in here calculates average seeking time if initial track number is either 0 or 499.

Any one wants to agree?