Page Replacement Definition – Page replacement policies decides that which type of page should be replaced, but these page replacement strategies are implemented when requested page is not existed into primary memory. Here, we will explain all page replacement algorithms.
Page Replacement Algorithms play vital role in the virtual memory management, because on the base of those Pages replacement policies can be specified that which memory block (page) should be swap out, arising memory space for needed page. Main objective of all Page replacement policies are to decrease the maximum number of page faults.
Page Fault – Page fault means memory error, and page fault occurs when currently programs try to access memory page for mapping into virtual address space, but it is not able to load into physical memory then it is known as “Page Fault”.
Types of Page Replacement Algorithms
There are various page replacement techniques, and we will explain each one
FIFO Page Replacement Algorithm
LIFO Page Replacement Algorithm
LRU Page Replacement Algorithm
Optimal Page Replacement Algorithm
Random Page Replacement Algorithm
FIFO Page Replacement Algorithm
This page replacement algorithm is very easy and simple because this algorithm is based on the “First in First out“principle. In which operating system uses the line as queue that store all information of all pages in the computer memory.
As per FIFO principle, oldest page is replaced at the front side and most recent page is replaced at the rear side.
Advantages of FIFO Page Replacement
It uses simple method, and easy to use.
It does not give more overhead.
Disadvantages of FIFO Page Replacement
Worst performance
Don’t use the frequency of last used time, just replace the oldest page.
Getting increase the page faults, while increasing page frames.
LIFO Page Replacement Algorithm
LIFO stands for “Last in First out“, and it performs all activities like LIFO principle. In this algorithm, newest page is replaced which is arrived at last in to primary memory, and it uses the stack for monitoring all pages.
LRU Page Replacement Algorithm
LRU stands for “Least Recently Used”, and it helps to operating system for searching such page that is used over the short duration of time frame. This page replacement algorithm uses the counter along with even page, and that counter is known as aging registers.
LRU algorithm helps to select that page which is not needed for long life in to primary memory.
Advantages of LRU Page Replacement
Most efficient
It helps to open for full analysis.
Easy to identify thefaulty page that is not needed to long time.
Not getting more suffers from Belady’s Anomaly.
Disadvantages of LRU Page Replacement
It has more complexity.
It has to need additional Data Structure.
More expensive
Need to highly hardware support.
Optimal Page Replacement Algorithm
Optimal Page Replacement Algorithm is very excellent page replacement policy because it helps to provide least number of page faults, so it is called of “OPT”, “Clairvoyant Replacement Algorithm”, and “Belady’s optimal page policy”.
Features are
In this algorithm, such pages are replaced which are not needed to long life duration in future.
