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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).
When pure demand paging is used, pages are loaded only when they are referenced. A program from a memory mapped file begins execution with none of its pages in RAM. As the program commits page faults, the operating system copies the needed pages from a file, e.g., memory-mapped file, paging file, or a swap partition containing the page data ...
This is known as demand paging. Some simpler real-time operating systems do not support virtual memory and do not need an MMU, but still need a hardware memory protection unit. Modern MMUs generally perform additional memory-related tasks as well.
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.
In operating systems that use virtual memory, every process is given the impression that it is working with large, contiguous sections of memory. Physically, the memory of each process may be dispersed across different areas of physical memory, or may have been moved ( paged out ) to secondary storage, typically to a hard disk drive (HDD) or ...
The operating system supports demand paging of virtual memory, which speeds up I/O for many applications. I/O device drivers use the Windows Driver Model . [ 143 ] The NTFS file system has a master table and each file is represented as a record with metadata . [ 144 ]
Similarly, a page frame is the smallest fixed-length contiguous block of physical memory into which memory pages are mapped by the operating system. [1] [2] [3] A transfer of pages between main memory and an auxiliary store, such as a hard disk drive, is referred to as paging or swapping. [4]
A system thrashing is often a result of a sudden spike in page demand from a small number of running programs. Swap-token [3] is a lightweight and dynamic thrashing protection mechanism. The basic idea is to set a token in the system, which is randomly given to a process that has page faults when thrashing happens.