GATE 2015 CS – Question 54
Consider a disk pack with a seek time of 4 milliseconds and rotational speed of 10000 rotations per minute (RPM). It has 600 sectors per track and each sector can store 512 bytes of data. Consider a file stored in the disk. The file contains 2000 sectors. Assume that every sector access necessitates a seek, and the average rotational latency for accessing each sector is half of the time for one complete rotation. The total time (in milliseconds) needed to read the entire file is ________.
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Correct answer: 14020
Explanation
One rotation takes $\frac{60000}{10000} = 6$ ms, so the average rotational latency is 3 ms. Reading one sector takes $\frac{6}{600} = 0.01$ ms. Each sector access costs $4 + 3 + 0.01 = 7.01$ ms, so the 2000 sectors take $2000 \times 7.01 = 14020$ ms.