置换算法，先进先出，在地址映射过程中，若在页面中发现所要访问的页面不在内存中，则产生缺页中断。当发生缺页中断时，如果操作系统内存中没有空闲页面，则操作系统必须在内存选择一个页面将其移出内存，以便为即将调入的页面让出空间。而用来选择淘汰哪一页的规则叫做页面置换算法。(In the process of address mapping, if page is found in the page, it is not in memory, resulting in page break. When there is a page break, if there is no free page in the operating system memory, the operating system must select a page in memory to remove it from the memory in order to give out space for the page to be transferred. The rule to choose which page to eliminate is called page replacement algorithm.)