Question

Given that main memory is composed of only three-page frames for public use and that a seven-page program (with pages a, b, c, d, e, f, g) that requests pages in the following order:

a, c, a, b, a, d, a, c, b, d, e, f

1)  Using the FIFO page removal algorithm, indicate the movement of the pages into and out of the available page frames (called a page trace analysis) indicating each page fault with an asterisk (*). Then compute the failure and success ratios.

​​​​2) Increase the size of memory so it contains four-page frames for public use. Using the same page requests as above and FIFO, do another page trace analysis and compute the failure and success ratios.

​​​​​​3)What general statement can you make from this example? Explain your answer.

Answer 1

1. FIFO Page Replacement Analysis:

Page Request: a, c, a, b, a, d, a, c, b, d, e, f

Available Page Frame = 3

Page Fault = 10

Hit Ratio = 2 / 12 = 0.17

Miss Ratio = 10 / 12 = 0.83

2. FIFO Page Replacement Analysis:

Page Request: a, c, a, b, a, d, a, c, b, d, e, f

Available Page Frame = 4

Page Fault = 6

Hit Ratio = 6 / 12 = 0.5

Miss Ratio = 6 / 12 = 0.5

3. The hit ratio increase when the available frame increase from 3 to 4 as given below:

Available frame = 3

Then, Hit Ratio = 0.17

Available frame = 4

Then, Hit Ratio = 0.5

But this is not the case in all scenario. When we increase the available frame then the hit ratio may decrease also.