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In computer operating systems, memory paging is a memory management scheme that eliminates the need for contiguous memory allocation. [1] [2] It is often combined with memory swapping, a technique where parts of a process can be swapped out of memory to secondary storage in order to allow the size of the physical address space to exceed the physical memory of the system.
Pages in the page cache modified after being brought in are called dirty pages. [5] Since non-dirty pages in the page cache have identical copies in secondary storage (e.g. hard disk drive or solid-state drive), discarding and reusing their space is much quicker than paging out application memory, and is often preferred over flushing the dirty pages into secondary storage and reusing their space.
PageDefrag is a program, developed by Sysinternals (now distributed by Microsoft), for Microsoft Windows that runs at start-up to defragment the virtual memory page file, the registry files and the Event Viewer's logs (files such as AppEvent.Evt, SysEvent.Evt, SecEvent.Evt and so on).
This would be time-consuming. It would be much faster if the reader had a listing of how many words are on each page. From this listing they could determine which page the 5,000th word appears on, and how many words to count on that page. This listing of the words per page of the book is analogous to a page table of a computer file system. [5]
If the virtual address is a valid page in a memory-mapped file or a paging file, a free page frame will be assigned and the page read in. In most cases, there will be an update to the page table, possibly followed by purging the Translation Lookaside Buffer (TLB), and the system restarts the instruction that causes the exception.
In this case the page is paged out to a secondary store located on a medium such as a hard disk drive (this secondary store, or "backing store", is often called a swap partition if it is a disk partition, or a swap file, swapfile or page file if it is a file). When this happens the page needs to be taken from disk and put back into physical memory.
Intel 5-level paging, referred to simply as 5-level paging in Intel documents, is a processor extension for the x86-64 line of processors. [1]: 11 It extends the size of virtual addresses from 48 bits to 57 bits by adding an additional level to x86-64's multilevel page tables, increasing the addressable virtual memory from 256 TiB to 128 PiB.
In computer operating systems, demand paging (as opposed to anticipatory paging) is a method of virtual memory management. In a system that uses demand paging, the operating system copies a disk page into physical memory only when an attempt is made to access it and that page is not already in memory ( i.e. , if a page fault occurs).