This document presents an overview of three page replacement algorithms: FIFO, LRU, and Optimal. Each algorithm is described along with example page requests and calculations of page hits, page faults, hit ratios, and miss ratios. The document also includes links for further problems related to these algorithms.

1. PAGE REPLACEMENT
ALGORITHMS
(FIFO/LRU/OPT)
A PRESENTATION BY ARIJIT ROY
COMPUTER SCIENCE & ENGG. DEPT., 2ND YEAR
HOOGHLY ENGINEERING & TECHNOLOGY COLLEGE

2. FIFO PAGE REPLACEMENT ALGORITHM
Suppose, all the page frames are filled with
different pages.
Now a new page request occurs.
This required page is not present in any
frame.
Then the page which came first, that will
swap out from the frame.
New page will swap in to that empty frame.

3. Q. Suppose there are page requests 5,2,3,2,7,1,3,4,5,1.
Assume there are 3 frames in RAM. Show the page
replacement by FIFO algorithm and calculate – number of
page hits and page faults, Hit ratio and miss ratio.
5 2 3 2 7 1 3 4 5 1

4. Q. Suppose there are page requests 5,2,3,2,7,1,3,4,5,1.
Assume there are 3 frames in RAM. Show the page
replacement by FIFO algorithm and calculate – number of
page hits and page faults, Hit ratio and miss ratio.
5 2 3 2 7 1 3 4 5 1
5 5
2
5
2
3
5
2
3
7
2
3
7
1
3 3
1
7 7
1
4 4
1
5 5
1
4
Page Hit Page Fault
No. of Page Hit = 3
No. of Page Fault = 7
 Hit Ratio = (No.
of Page Hit /
Total Pages) =
3/10
 Miss Ratio =
(No. of Page
Fault / Total
Pages) = 1- Hit
Ratio = 7/10

5. LRU PAGE REPLACEMENT ALGORITHM
Suppose, all the page frames are filled with
different pages.
Now a new page request occurs.
This required page is not present in any
frame.
Then the page which is least recently used
that will swap out.
New page will swap in to that empty frame.

6. Q. Suppose there are page requests 2,3,1,2,4,1,6,2,5,4.
Assume there are 3 frames in RAM. Show the page
replacement by LRU algorithm and calculate – number of
page hits and page faults, Hit ratio and miss ratio.
2 3 1 2 4 1 6 2 5 4

7. Q. Suppose there are page requests 2,3,1,2,4,1,6,2,5,4.
Assume there are 3 frames in RAM. Show the page
replacement by LRU algorithm and calculate – number of
page hits and page faults, Hit ratio and miss ratio.
2 3 1 2 4 1 6 2 5 4
2 2 2 2 2 2 6 6 6 4
2
55111111
3 3 3 4 4 4 2 2
No. of Page Hit = 2
No. of Page Fault = 8
 Hit Ratio = (No.
of Page Hit /
Total Pages) =
2/10 = 1/5
 Miss Ratio = (No.
of Page Fault /
Total Pages) = 1 –
Hit Ratio = 8/10 =
4/5Page Hit Page Fault

8. OPTIMAL PAGE REPLACEMENT ALGORITHM
Suppose, all the page frames are filled with
different pages.
Now a new page request occurs.
This required page is not present in any
frame.
Then the page which is used most later that
will swap out.
New page will swap in to that empty frame.

9. Q. Suppose there are page requests 2,1,5,3,4,2,5,1,2,5.
Assume there are 3 frames in RAM. Show the page
replacement by Optimal page replacement algorithm and
calculate – number of page hits and page faults, Hit ratio and
miss ratio.
2 1 5 3 4 2 5 1 2 5

10. Q. Suppose there are page requests 2,1,5,3,4,2,5,1,2,5.
Assume there are 3 frames in RAM. Show the page
replacement by Optimal page replacement algorithm and
calculate – number of page hits and page faults, Hit ratio and
miss ratio.
2 1 5 3 4 2 5 1 2 5
Page FaultPage Hit
2 2
1
5
2
1
5
2
3
5
4
2 2
4
5
2
4
5
2
1
5
2
1
5
2
1
5
3 is not present. So it will use in far future.4 is not present. So it will use in further future.
No. of Page Hit = 4
No. of Page Fault = 6
 Hit Ratio = (No.
of Page Hit /
Total Pages) =
4/10 = 2/5
 Miss Ratio = (No.
of Page Fault /
Total Pages) = 1 –
Hit Ratio = 6/10 =
3/5

11. THAT’S ALL FOR THE DAY
There is a set of problems from this algorithms
are already given. You can download it from the
link given below.
Link - https://drive.google.com/open?id=10kDzksl-
aaPcAESSTB3f30nnxBDhftvL
Link is also given in description box.
You can mail me the answer sheet on
byte2bytelearn@gmail.com

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