Mail Archives: djgpp/1998/04/03/11:31:53
"MNR. LE SMITH" <9813152 AT fharga DOT sun DOT ac DOT za> wrote:
> i have recently read a few articles concerning protected mode etc.
>
> but i still have not yet figured out what the difference is between
> linear- and physical address pointers.
>
> could someone please (briefly) explain to me what the difference is
> between linear and physical memory addresses.
386 processors supports the 2 most common protection schemes:
1) Segmentation.
2) Pagination.
When the processor uses pages the memory is subdivided in blocks of the same
and fixed size called pages. Normally 4Kb (386 support another size too if I
remmember well). Each page is located at a physical address and have an entry
in one table. This entry says the right access and where this page is mapped in
the linear space. So you can remap the address, the linear address may be the
same as the physical or not. A good example is the virtual memory: You have
more pages in the table than physical pages in RAM, the OS swaps to disk the
less used pages and keeps in memory the more commonly used pages. As you can
see here some physical page is mapped to one address that isn't the same linear
address all the time.
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