Page Replacement Algorithms in OS (operating System)
Definition – Page replacement policies in OS lets decide 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.
Why to Need of Page Replacement Algorithms
Page Replacement Algorithms play essential function within the virtual reminiscence control, due to the fact on the bottom of those Pages replacement guidelines can be targeted that which memory block (page) ought to be swap out, springing up memory space for needed web page. Main goal of all Page replacement regulations are to lower the maximum variety of page faults is used in operating system.
Page Fault – Page fault way reminiscence errors, and page fault takes place whilst currently programs attempt to get right of entry to reminiscence web page for mapping into virtual address area, but it isn't able to load into physical reminiscence then it's far referred to as “Page Fault”, ans acts like as mobile computing as well.
Types of Page Replacement Algorithms
There are numerous page substitute strategies, and we will provide an explanation for every 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 web page replacement algorithm may be very easy and easy due to the fact this algorithm is primarily based on the “First in First out“precept. In which running gadget makes use of the line as queue that store all statistics of all pages within the laptop reminiscence.
As in line with FIFO precept, oldest page is changed on the front facet and maximum current page is replaced on the rear aspect.
Advantages of FIFO Page Replacement
• It makes use of easy approach, and smooth to use.
• It does now not deliver more overhead.
Disadvantages of FIFO Page Replacement
• Worst overall performance
• Don’t use the frequency of ultimate used time, simply replace the oldest page.
• Getting growth 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 precept. In this algorithm, latest page is replaced which is arrived at last in to number one memory, and it uses the stack for tracking all pages.
LRU Page Replacement Algorithm
LRU stands for “Least Recently Used”, and it enables to operating gadget for searching such web page that is used over the quick length of time body. This web page alternative set of rules makes use of the counter along with even web page, and that counter is known as getting old registers.
LRU set of rules helps to pick out that web page which is not wanted for lengthy lifestyles in to number one memory.
Advantages of LRU Page Replacement
• Most efficient
• It helps to open for complete evaluation.
• Easy to perceive the faulty web page that isn't needed to long time.
• Not getting greater suffers from Belady’s Anomaly.
Disadvantages of LRU Page Replacement
• It has more complexity.
• It has to need extra Data Structure.
• More pricey
• Need to enormously hardware assist.
Optimal Page Replacement Algorithm
Optimal Page Replacement Algorithm may be very brilliant web page alternative policy as it allows to offer least variety of web page faults, so it's far known as of “OPT”, “Clairvoyant Replacement Algorithm”, and “Belady’s premiere page policy”.
Features are
• In this algorithm, such pages are changed which aren't needed to long existence period in destiny.
• This algorithm does not produce greater page faults.
• It has very low page fault rate compare to different set of rules.
Advantages of Optimal Page Replacement
• Easy to use
• Easy to put into effect facts systems for pleasant end result
• Excellent performance
• Less complexity
• Less need to assistance
Disadvantages of Optimal Page Replacement
• More time consumption
• Need future awareness of program.
• Difficult to errors handling
• Not easy to implement, because O/S now not able to hint future request.
Random Page Replacement Algorithm
In this set of rules, randomly web page may be changed anytime, however it works like different page alternative coverage which include FIFO, LIFO, LRU and Optimal.
