Discussion
Consider a process executing on an operating system that uses demand paging. The average time for a memory access in the system is \(M\) units if the corresponding memory page is available in memory, and \(D\) units if the memory access causes a page fault. It has been experimentally measured that the average time taken for a memory access in the process is \(X\) units.
Which one of the following is the correct expression for the page fault rate experienced by the process?
Answer: B
The page fault rate is \((X - M) / (D - M)\).
If \(p\) is the page fault rate, a fraction \(p\) of accesses take \(D\) units and the rest take \(M\) units, so the measured average is
\[ \begin{aligned} X &= (1 - p)M + pD \\ X - M &= p(D - M) \\ p &= \frac{X - M}{D - M} \end{aligned} \]
Check: if no access faults, \(X = M\) and \(p = 0\); if every access faults, \(X = D\) and \(p = 1\). The option \((D - M)/(X - M)\) is the reciprocal and exceeds 1. \((D - X)/(D - M)\) is the hit rate \(1 - p\), and \((X - M)/(D - X)\) is the ratio of faults to hits.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development