Clock - Second Chance with a circular list. First time a page is considered, its referenced bits are cleared so it will be chosen the second time around. The idea here is that programs exhibit code and data locality , that is they frequently reuse the same data or code. Use hardware counters, matrix. Basically this is LRU with only one bit.
Clean pages get preference in being paged out.
Theory of Page Replacement Paging algorithms are analyzed by studying the effects of the algorithm on reference strings - that is sequences of page references against which the algorithm is studied. In the FIFO case above, there are different contents in the upper 3 page frames in memory for several states. FIFO is not a stack algorithm. Any non-stack algorithm can display Belady's anomaly. LRU is a stack algorithm.