Chapter 1, Problem 17CRP

Explanation of Solution

Determine the average access time for a hard disk:

To find the period rotation, only a half rotation is required.

Consider the rotations of the hard disk as $360\text{revolutions}\text{per}\text{second}$.

• Period of rotation is equal to inverse of number of revolution per second.

  $\text{Period}\text{of}\text{rotation}=\left(\frac{1}{\text{number}\text{of}\text{revolution}}\right)\text{s}$

• Substitute $360$ for number of revolutions per section in the above equation.

  $\begin{array}{c}\text{Period}\text{of}\text{rotation}=\left(\frac{1}{360}\right)\text{s}\\ =0.00277\text{s}\left(\frac{{10}^3\text{ms}}{1\text{s}}\right)\\ =2.77\text{s}\end{array}$

• Since, average Latency time is half of the period of rotation. Therefore, the average latency time is calculated as,

$\begin{array}{c}\text{Average}\text{Latency}\text{Time}=\frac{1}{2}\times (2\end{array}$