Page Replacement is a very important topic in memory management. It is a part of the Operating System as well as Computer Architecture. There are so many page replacement algorithms. These 3 are too important algorithms. If you have any doubt regarding this, then you can mail me at - byte2bytelearn@gmail.com Youtube Channel Link - https://youtu.be/BoXrIOs2itc Facebook Page Link - https://www.facebook.com/byte2bytelearn/ Twitter Link - https://twitter.com/bytes_learning Stay tuned with Learning Bytes. I will upload more videos and slides.

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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