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Demand paging. 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).
Memory paging. 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. [citation needed] In this scheme, the operating system retrieves data from secondary storage in same-size blocks called ...
mmap. In computing, mmap(2) is a POSIX -compliant Unix system call that maps files or devices into memory. It is a method of memory-mapped file I/O. It implements demand paging because file contents are not immediately read from disk and initially use no physical RAM at all. The actual reads from disk are performed after a specific location is ...
Memory management unit. A memory management unit ( MMU ), sometimes called paged memory management unit ( PMMU ), [1] is a computer hardware unit that examines all memory references on the memory bus, translating these requests, known as virtual memory addresses, into physical addresses in main memory . In modern systems, programs generally ...
Virtual memory combines active RAM and inactive memory on DASD [a] to form a large range of contiguous addresses. In computing, virtual memory, or virtual storage, [b] is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" [3] which "creates the illusion ...
In operating systems, memory management is the function responsible for managing the computer's primary memory. [1] : 105–208. The memory management function keeps track of the status of each memory location, either allocated or free. It determines how memory is allocated among competing processes, deciding which gets memory, when they ...
In a computer operating system that uses paging for virtual memory management, page replacement algorithms decide which memory pages to page out, sometimes called swap out, or write to disk, when a page of memory needs to be allocated. Page replacement happens when a requested page is not in memory ( page fault) and a free page cannot be used ...
Thrashing (computer science) In computer science, thrashing occurs in a system with virtual memory when a computer's real storage resources are overcommitted, leading to a constant state of paging and page faults, slowing most application -level processing. [1] This causes the performance of the computer to degrade or collapse.