In Virtual memory management, demostrate one of the page replacement algorithms.

Optimal Page Replacement

An optimal page-replacement algorithm has the lowest page-fault rate of all algorithms and will never suffer from Belady's anomaly.Such an algorithm does exist and has been called OPT or MIN.It is simply this:

Replace the page that will not be used

for the longest period of time

use of this page-replacement algorithm guarantees the lowest possible page-fault rate for a fixed number of frames.

For example :

we get a reference string :7 0 1 2 0 3 0 4 2 3 2 1 2 0.....

and our page has 3 frames

first we can fill the three empty frames with 7 0 1

and then we should traverse the string and we can find a reference that will not be used for the longest period of time is:7

so the second step is convert the first frame to 2...

 

 

So as we mentioned above , the most important point of this Page Replacement algorithm is that , we have to predict the future

and then it can find the most useless resource in the future. It's a difficult and too idealized method.