demand paging


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demand paging

[də′mand ‚pā·jiŋ]
(computer science)
The characteristic of a virtual memory system which retrieves only that part of a user's program which is required during execution.

demand paging

(memory management)
A kind of virtual memory where a page of memory will be paged in if an attempt is made to access it and it is not already present in main memory. This normally involves a memory management unit which looks up the virtual address in a page map to see if it is paged in. If it is not then the operating system will page it in, update the page map and restart the failed access. This implies that the processor must be able to recover from and restart a failed memory access or must be suspended while some other mechanism is used to perform the paging.

Paging in a page may first require some other page to be moved from main memory to disk ("paged out") to make room. If this page has not been modified since it was paged in, it can simply be reused without writing it back to disk. This is determined from the "modified" or "dirty" flag bit in the page map. A replacement algorithm or policy is used to select the page to be paged out, often this is the least recently used (LRU) algorithm.

Prepaging is generally more efficient than demand paging.

demand paging

Copying a page of program code from disk into memory when required by the program.
References in periodicals archive ?
The demand paging variant of post-copy is the simplest and slowest option.
Thus, each page is transferred only once, either by demand paging or by an active push.
Demand Paging reportedly optimises memory utilisation, which enables more efficient usage of RAM by loading read-only code and data only when required ('on demand'), allowing consumers to launch applications faster and keep multiple applications open simultaneously.
These include the choice of page size, the role of prepaging as compared with demand paging, and the exploitation of techniques for improving the locality of information, so that fewer pages need to be loaded into high-speed memory.
Within the scope of the deal lies also the mission to further develop the functionality for demand paging which is found in the latest release of Enea OSE 5.
With the steady increase of software in mobile phones demand paging is an important functionality to further optimize the usage of RAM-memory and thus bring down the bill of materials.
This considerably reduces the amount of demand paging needed to run most applications (reading and writing of data to the page file on the hard disk), thereby noticeably improving application responsiveness.
The BinFS implements a demand paging mechanism for the OS files that enable a faster boot process, significantly lower RAM allocation, and a safer operation.
Because of VisualSQRIBE's demand paging capabilities, only the desired pages are downloaded to the browser, speeding performance.