Скачать или смотреть L-2.3 Page Replacement Algorithm Solution (PU) of year 2019 Fall in Nepali

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Page replacement algorithm: -

A page replacement algorithm is a mechanism used by the operating system to decide which page(s) in memory should be removed when new page(s) need to be loaded. The goal is to choose the page(s) that will not be used for the longest period of time in the future, in order to minimize the number of page faults. Some common page replacement algorithms include:

1) First In First Out (FIFO) : Replace the page that has been in the memory for Longest time.
In simple, Replace the page which comes first in the memory frames.

2) Optimal Page Replacement (OPT or MIN) : The Optimal page replacement algorithm, also known as MIN (Minimum page to be used in future) algorithm, is a page replacement algorithm that always selects the page that will not be used for the longest period of time in the future for replacement. In other words, it selects the page with the farthest-future use time for replacement. This algorithm is considered to be the best possible page replacement algorithm, as it always selects the page that will lead to the least number of page faults.

3) Least Recently Used (LRU) : The Least Recently Used (LRU) page replacement algorithm is a page replacement algorithm that selects the page that has been used least recently for replacement. The idea is that if a page has not been used recently, it is unlikely to be used in the near future.

4) Second Chance (Clock): A "second chance algorithm" is a variation of the FIFO (First In, First Out) page replacement algorithm used in operating systems to manage memory. When a page is first loaded into memory, its reference bit is set to 0. Every time the page is referenced (e.g., read from or written to), the bit is set to 1. When the system needs to free up a page of memory, it begins by looking at the page at the front of the queue. If the reference bit for that page is 0, it is removed from memory. If the reference bit is 1, it gets the second chance.

5) Least Frequently Used (LFU) : Least Frequently Used (LFU) is a page replacement algorithm used in operating systems to manage memory. The basic idea behind LFU is to keep track of how often each page is used and remove the page that has been used the least number of times when the system needs to free up a page of memory.

LFU algorithm works by keeping a counter for each page, which is incremented each time the page is referenced. When the system needs to free up a page of memory, it selects the page with the lowest count and removes it from memory.

6) Most Recently Used (MRU) : The Most Recently Used (MRU) algorithm is a page replacement algorithm that replaces the page that was most recently used. The operating system keeps track of when each page was last accessed and replaces the page that was accessed most recently.

7) Most Frequently Used (MFU) : The Most Frequently Used (MFU) algorithm is a page replacement algorithm that replaces the page that has been used most frequently. The operating system keeps track of how many times each page has been accessed, and replaces the page that has been accessed the most number of times.

Note:
In memory, if there is same string then it is Hit.
And if memory frames are empty and there is different string in memory then it is Miss


Page Fault:
A page fault is an event that occurs when a program requests a page of memory that is not currently in main memory (RAM) and must be retrieved from auxiliary memory, such as a hard disk or a network file system. The process of resolving a page fault is called page swapping, paging or swapping. Page faults can occur for a number of reasons, including:

A page is not present in main memory because-
. it was never accessed before.
.it was replaced by another page according to the page replacement algorithm used by the operating system.
.it was swapped out to make room for another page.
In general, too many page faults can cause the performance of a system to degrade, especially if the page faults are caused by insufficient physical memory. To reduce page faults, an operating system can use page replacement algorithms or add more physical memory.

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