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SubjectRe: large memory support for x86
** Reply to message from Jeff Epler <jepler@inetnebr.com> on Thu, 12 Oct 2000
13:08:19 -0500


> What the support for >4G of memory on x86 is about, is the "PAE", Page Address
> Extension, supported on P6 generation of machines, as well as on Athlons
> (I think). With these, the kernel can use >4G of memory, but it still can't
> present a >32bit address space to user processes. But you could have 8G
> physical RAM and run 4 ~2G or 2 ~4G processes simultaneously in core.

How about the kernel itself? How do I access the memory above 4GB inside a
device driver?

> There may or may not be some way to support an abomination like the old "far"
> pointers in DOS (multiple 4G segments), but I don't think it has been written
> yet.

Yes, it's ugly, but it works and it's compatible. Well, compatible with 32-bit
code, probably not compatible with Linux code overall.

Of course, you could define a pointer to be a 48-bit value, but I doubt that
would really work.






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Timur Tabi - ttabi@interactivesi.com
Interactive Silicon - http://www.interactivesi.com

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