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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).
While this article concentrates on modern MMUs, commonly based on demand paging, early systems used base and bounds addressing that further developed into segmentation, or used a fixed set of blocks instead of loading them on demand. The difference between these two approaches is the size of the contiguous block of memory; paged systems break ...
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 to users of a very large (main) memory".
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 ...
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. Virtual addresses are used by the program executed by the accessing process , while physical addresses are used by the hardware, or more specifically, by the random-access memory (RAM) subsystem.
A page, memory page, or virtual page is a fixed-length contiguous block of virtual memory, described by a single entry in a page table.It is the smallest unit of data for memory management in an operating system that uses virtual memory.
The (h,k)-paging problem is a generalization of the model of paging problem: Let h,k be positive integers such that . We measure the performance of an algorithm with cache of size h ≤ k {\displaystyle h\leq k} relative to the theoretically optimal page replacement algorithm .
The main difference between System V shared memory (shmem) and memory mapped I/O (mmap) is that System V shared memory is persistent: unless explicitly removed by a process, it is kept in memory and remains available until the system is shut down. mmap'd memory is not persistent between application executions (unless it is backed by a file).