Question

<Operating System>

1. A process accesses pages in the following order (Assume all frames are initially empty):

1 2 3 4 2 1 5 6 2 1 2 3 7 6 3 2 1 2 3 6 Determine the number of page faults that will occur for the following algorithms: (Show your work!)

1. Least Recently Used replacement algorithm with 5 frames available to the process.
   2. What is the minimum number of page faults that can occur for this process, regardless of algorithm or number of available frames? Why?

**NO IMAGE PLEASE**

Answer 1

Least Recently Used Algorithm :-

Least Recently Used (LRU) algorithm is a Greedy calculation where the page to be supplanted is least as of late utilized.The thought depends on region of reference, the least as of late utilized page can't.

At whatever point another page is referred and not present in memory, Page Fault happens and Operating System replaces one of the current pages with recently required page.

Page Hit occurs when the new incoming page is found in one of the existing Pages.

Let say the page reference string 1 2 3 4 2 1 5 6 2 1 2 3 7 6 3 2 1 2 3 6 .

Initially we have 5 page slots empty.

Request	1	2	3	4	2	1	5	6	2	1
Frame5							5	5	5	5
Frame4				4	4	4	4	4	4	4
Frame3			3	3	3	3	3	6	6	6
Frame2		2	2	2	2	2	2	2	2	2
Frame1	1	1	1	1	1	1	1	1	1	1
Hit/Fault	Fault	Fault	Fault	Fault	Hit	Hit	Fault	Fault	Hit	Hit

Request	2	3	7	6	3	2	1	2	3	6
Frame5	5	5	7	7	7	7	7	7	7	7
Frame4	4	3	3	3	3	3	3	3	3	3
Frame3	6	6	6	6	6	6	6	6	6	6
Frame2	2	2	2	2	2	2	2	2	2	2
Frame1	1	1	1	1	1	1	1	1	1	1
Hit/Fault	Hit	Fault	Fault	Hit	Hit	Hit	Hit	Hit	Hit	Hit

No. of Page fault:- 8

No. of Page Hit:- 12

Optimal Page Replacement Algorithm is the another page replacement algorithm. This Page Replacement Algorithm gives the minimum no. of page faults because in this algorithm, OS replaces the page that will not be utilized for the longest period of time in future.Therefore, this gives the minimum no. Of Page Faults.

In Addition to this, if the above given numerical is tried to solve by Optimal Page Replacement Algorithm then the Page fault is 7 which is minimum in all of the algorithms.