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If a disk has seek time of 20 ms, rotates  20 revolutions per second, has 100 words per block, and each track has capacity of 300 words. Then total time required to access one block is
A. 25
B. 30
C. 40
D. 60

1 Answer

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$T_{data\_transfer\_rate}$ $ = Track\_Capacity \times R\\ =300 \times 20\\ =6000\ \ words/sec$

Time req. to transfer 100 word block:
$T_{overhead}$ $ = \frac{100}{6000}\\ =0.01667 \ \ sec\\ =16.67 \ \ msec$

$T_{rotational\_delay}$ $ = \frac{1}{2} \times \frac{1}{20}\\ =0.025 \ \ sec\\ =25 \ \ msec$

Total time req. to acces one block:

$T$ $ = T_{seek\_time} + T_{rotational\_dealy} +T_{overhead}\\ =20 + 25+16.67\\ = 61.67 \ \ msec$

So, answer is option D

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