Given that main memory is composed of only three page frames for public use and

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

a. 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 ratio and success ratio.

b.    Using FIFO again, increase the size of memory so it contains four page frames for public use. Using the same page requests as above, do another page trace analysis and compute the failure and success ratios.

                  c. What general statement can you make from this example? Explain your answer.

Explanation / Answer

So we are using the FIFO page removal.This means the page that comes first goes out first.

The sequence is a,b,c,b,d,a,e,f,b,e,d,f

Assuming at the start three pages are already loaded

Requset page      Pages in Memory            Success/Failure
a                   a,b,c                         S
b                   a,b,c                         S
c                   a,b,c                         S
b                   a,b,c                         S
d                   b,c,d                         F (a - out, d-in)
a                   c,d,a                         F (b - out, a-in)
e                   d,a,e                         F (c - out, e-in)
f                   a,e,f                         F (d - out, f-in)
b                   e,f,b                         F (a - out, b-in)
e                   e,f,b                         S
d                   f,b,d                         F (e - out, d-in)
f                   f,b,d                         S

number of faults = 6
numbert of success = 6

For 4 page frames
Assuming at the start four pages are already loaded

Requset page      Pages in Memory            Success/Failure
a                   a,b,c,d                       S
b                   a,b,c,d                       S
c                   a,b,c,d                       S
b                   a,b,c,d                       S
d                   a,b,c,d                       S
a                   a,b,c,d                       S
e                   b,c,d,e                       F (a - out, e-in)
f                   c,d,e,f                       F (b - out, f-in)
b                   d,e,f,b                       F (c - out, b-in)
e                   d,e,f,b                       S
d                   d,e,f,b                       S
f                   d,e,f,b                       S

number of faults = 3
number of success = 9

So in genrral we can conclude that if the number of page frames is high,
we will less faults and more success

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