Paging: Difference between revisions

Paging (view source)

Revision as of 19:07, 2 December 2009

227 bytes added , 14 years ago

Made x86-specific references obvious in the new overview. Added cross-reference to Segmentation.

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osdev>Aj

Revision as of 17:08, 30 November 2009 (view source) osdev>Aj (Tried to fix overview paragraph.) ← Older edit		Revision as of 19:07, 2 December 2009 (view source) osdev>Aj (Made x86-specific references obvious in the new overview. Added cross-reference to Segmentation.) Newer edit →
Line 2: 32 bit x86 processors support a 4GiB virtual address space and current 64 bit processors support a 256TiB virtual address space (with a theoretical maximum of 16EiB). Paging is a system which allows each process to see the full virtual address space, without actually requiring the full amount of physical RAM to be physically installed. In fact, current implementations of x86-64 has a current physical RAM limit of 1TiB and a theoretical limit of 4PiB of physical RAM. In addition to this, paging introduces the benefit of page-level protection. In this system, user-level ~~(ring 3)~~ processes can only see and modify data which is paged in to their own address space, providing hardware isolation. System pages are also protected from user processes. On the x86-64 architecture, page-level protection now completely supercedes [[Segmentation]] as the memory protection mechanism. On the IA32 architecture, both paging and segmentation exist, but segmentation is now considered 'legacy'. Once an Operating System has paging, it can also make use of other benefits and workarounds, such as linear framebuffer simulation for memory-mapped IO and paging out to disk, where disk storage space is used to free up physical RAM.