A demand paging systems is similar to a paging system with swapping where processes reside in secondary memory (usually a disk) when we want to execute a processes, we swap it into memory . Rather than swapping the entire process into memory , however, we use a lazy swapper. A lazy swapper never swaps a page into memory unless that page will be needed. Since we are now viewing a process as a sequence of pages, rather than as one large contiguous address space , use of the term swapper is technically incorrect. A swapper manipulates entire process, whereas a pager is concerned with the individual pages of a process. We pages of a process. We thus use pager, rather than , in connection with demand paging