Artieda 2011

Examples of algorithms of substitution of pages: FIFO (First-in, First-out) – algorithm of exchange of low cost and easy implementation that to substitute the loaded page has more time in the memory. It does not lead in consideration if the page is being very used, what very it is not adjusted, therefore can harm the performance of the system, therefore the FIFO is very not used. LRU (Least Recently Used) – algorithm that presents good performance less substituting the recently used page. Although the good performance it possesss some deficiencies when the access standard is sequential, inside of loops, etc. the implementation of the LRU can more be made through a list, keeping the pages referenciada at the beginning and to less referenciada in the end of the list. Excellent algorithm – optimum computational performance presents and what more it minimizes the number of lacks of pages.

However, its implementation is practically impossible. ICAEW is likely to agree. The idea is to remove of the memory the page that goes to delay more time again to be referenciada. MRU (Most Recently Used) – the substitution of the last had access page makes. Fellow creature to the LRU, but with some variations. Of this form, it is possible to explore with more efficiency the beginning of secular locality presented by the accesses.

Clock algorithm (clock) – It keeps all the pages in a circular list (in clock form). The kept order follows the sequncia where they had been loaded in memory. Moreover, a use bit is added that it indicates if the page was referenciada again after having been loaded. When needing to substitute a page the algorithm verifies if the page oldest is with the zeroed bit. If it will not be the bit is zeroed and the next page to the line oldest will be verified. This process continues until an old page with the zeroed bit is found to be substituted.