paged ==>
paging
<operating system> A technique for increasing the memory space available
by moving infrequently-used parts of a program's working memory from RAM to a
secondary storage medium, usually hard {disk. The unit of transfer is called a
page.
A memory management unit (MMU) monitors accesses to memory and splits each
address into a page number (the most significant bits) and an offset within that
page (the lower bits). It then looks up the page number in its page table. The
page may be marked as paged in or paged out. If it is paged in then the memory
access can proceed after translating the virtual address to a physical address.
If the requested page is paged out then space must be made for it by paging out
some other page, i.e. copying it to disk. The requested page is then located on
the area of the disk allocated for "swap space" and is read back into RAM. The
page table is updated to indicate that the page is paged in and its physical
address recorded.
The MMU also records whether a page has been modified since it was last paged
in. If it has not been modified then there is no need to copy it back to disk
and the space can be reused immediately.
Paging allows the total memory requirements of all running tasks (possibly just
one) to exceed the amount of physical memory, whereas swapping simply allows
multiple processes to run concurrently, so long as each process on its own fits
within physical memory.
(1996-11-22)
Nearby terms:
Page Mode Dynamic Random Access Memory « page out «
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paging » PaiLisp » pain in the net » Paintbrush
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