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In computer operating systems, memory paging (or swapping on some Unix-like systems) is a memory management scheme by which a computer stores and retrieves data from secondary storage [a] for use in main memory. [1]
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).
The theoretically optimal page replacement algorithm (also known as OPT, clairvoyant replacement algorithm, or Bélády's optimal page replacement policy) [3] [4] [2] is an algorithm that works as follows: when a page needs to be swapped in, the operating system swaps out the page whose next use will occur farthest in the future. For example, a ...
Thrashing occurs when there are too many pages in memory, and each page refers to another page. Real memory reduces its capacity to contain all the pages, so it uses 'virtual memory'. When each page in execution demands that page that is not currently in real memory (RAM) it places some pages on virtual memory and adjusts the required page on RAM.
A system with a smaller page size uses more pages, requiring a page table that occupies more space. For example, if a 2 32 virtual address space is mapped to 4 KiB (2 12 bytes) pages, the number of virtual pages is 2 20 = (2 32 / 2 12). However, if the page size is increased to 32 KiB (2 15 bytes), only 2 17 pages are required. A multi-level ...
4-level paging of the 64-bit mode. In the 4-level paging scheme (previously known as IA-32e paging), the 64-bit virtual memory address is divided into five parts. The lowest 12 bits contain the offset within the 4 KiB memory page, and the following 36 bits are evenly divided between the four 9 bit descriptors, each linking to a 64-bit page table entry in a 512-entry page table for each of the ...
Pagination, also known as paging, is the process of dividing a document into discrete pages, either electronic pages or printed pages.. In reference to books produced without a computer, pagination can mean the consecutive page numbering to indicate the proper order of the pages, which was rarely found in documents pre-dating 1500, and only became common practice c. 1550, when it replaced ...
Physical memory can contain pages belonging to many processes. Pages can be held on disk if seldom used, or if physical memory is full. In the diagram above, some pages are not in physical memory. A page table is a data structure used by a virtual memory system in a computer to store mappings between virtual addresses and physical addresses.