when physical memory is not full this is a simple operation; the page is written back into physical memory, the page table and tlb are updated, and the instruction is restarted. however, when physical memory is full, one or more pages in physical memory will need to be paged out to make room for the requested page. the page table needs to be updated to mark that the pages that were previously in physical memory are no longer there, and to mark that the page that was on disk is now in physical memory. the tlb also needs to be updated, including removal of the paged-out page from it, and the instruction restarted. which page to page out is the subject of page replacement algorithms.