Chapter 3, Problem 23CRP

Explanation of Solution

Determine how much time slice is required to wait for read operation:

The allotted time slice is 50 milliseconds, the time taken to position read/write head over the desired track is 8 milliseconds and the another 17 milliseconds are required for the desired data to rotate around the read or write head.

• To find the waiting time to read, add 8 milliseconds with 17 milliseconds as shown below:

  $\begin{array}{c}\text{Wating}\text{time}\text{to}\text{read}=8\text{milliseconds}+17\text{milliseconds}\\ =\text{25}\text{milliseconds}\end{array}$

• Thus, the waiting time to read is 25 milliseconds.
• To find the part of time slice required to wait for read operation, divide the waiting time to read by the allotted time slice.

  $\text{The}\text{part}\text{of}\text{time}\text{slice}\text{required}\text{to}\text{wait}\text{for}\text{read}=\frac{\text{Wating}\text{time}\text{to}\text{read}}{\text{Alloted}\text{time}\text{slice}}$

  Substitute 25 milliseconds for waiting time to and 50 milliseconds for allotted time slice.

  $\begin{array}{c}\text{The}\text{part}\text{of}\text{time}\text{slice}\text{required}\text{to}\text{wait}\text{for}\text{read}\text{operation}=\frac{25\text{milliseconds}}{\text{50}\text{milliseconds}}\\ =\frac{1}{2}\text{of}\text{time}\text{slice}\end{array}$

Therefore, the required part of time slice to wait for the read operation is “$\frac{1}{2}$”.

Determine how many instructions can be executed during waiting period.

The machine is capable of executing 10 instructions each nanoseconds, that is $10\text{instructions}=1\text{nanosecond}$.

• To find the number of instruction that could be executed per second, divide 10 instructions by 1 nanosecond