FIFO, LRU, OPTIMAL Page Replacement Algorithm

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

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.

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

replacement by FIFO algorithm and calculate – number of
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

LRU PAGE REPLACEMENT ALGORITHM
different pages.
frame.
Then the page which is least recently used
that will swap out.

replacement by LRU algorithm and calculate – number of
2 3 1 2 4 1 6 2 5 4

replacement by LRU algorithm and calculate – number of
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
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

OPTIMAL PAGE REPLACEMENT ALGORITHM
different pages.
frame.
Then the page which is used most later that
will swap out.

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

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
of Page Hit /
Total Pages) =
4/10 = 2/5
 Miss Ratio = (No.
of Page Fault /
Total Pages) = 1 –
Hit Ratio = 6/10 =
3/5

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

HOPE YOU GUYS ENJOY THIS SLIDE.
SEE YOU IN THE NEXT VIDEO.
STAY HOME, STAY SAFE.

FIFO, LRU, OPTIMAL Page Replacement Algorithm

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