<P> NRU is a marking algorithm, so it is k k − h + 1 (\ displaystyle (\ dfrac (k) (k - h + 1))) - competitive . </P> <P> The simplest page - replacement algorithm is a FIFO algorithm . The first - in, first - out (FIFO) page replacement algorithm is a low - overhead algorithm that requires little bookkeeping on the part of the operating system . The idea is obvious from the name--the operating system keeps track of all the pages in memory in a queue, with the most recent arrival at the back, and the oldest arrival in front . When a page needs to be replaced, the page at the front of the queue (the oldest page) is selected . While FIFO is cheap and intuitive, it performs poorly in practical application . Thus, it is rarely used in its unmodified form . This algorithm experiences Bélády's anomaly . In simple words, on a page fault, the frame that has been in memory the longest is replaced . </P> <P> FIFO page replacement algorithm is used by the VAX / VMS operating system, with some modifications . Partial second chance is provided by skipping a limited number of entries with valid translation table references, and additionally, pages are displaced from process working set to a systemwide pool from which they can be recovered if not already re-used . </P> <P> FIFO is a conservative algorithm, so it is k k − h + 1 (\ displaystyle (\ dfrac (k) (k - h + 1))) - competitive . </P>

What is optimal page replacement in operating system