Re: PAE and PSE ??

H. Peter Anvin
2006-10-23T14:10:59Z

Rafael J. Wysocki wrote:
>
> Well, "AMD64 Architecture Programmer’s Manual" says the following:
>
> The choice of 2 Mbyte or 4 Mbyte as the large physical-page size
> depends on the value of CR4.PSE and CR4.PAE, as follows:
> - If physical-address extensions are enabled (CR4.PAE=1), the
> large physical-page size is 2 Mbytes, regardless of the value
> of CR4.PSE.
> - If physical-address extensions are disabled (CR4.PAE=0)
> and CR4.PSE=1, the large physical-page size is 4 Mbytes.
> - If both CR4.PAE=0 and CR4.PSE=0, the only available page
> size is 4 Kbytes.
>

That would be a retroactive redef on the part of AMD; it probably makes
sense for x86-64 if someone thinks that is may drop support for 4 MB
pages at some point in the distant future. Still, I'm not sure Intel
would agree with the definition as stated, although I haven't looked in
the docs.

This is all extremely theoretical, since there has never been a chip
with PAE=1 and PSE=0, and I wouldn't expect one to appear any time soon.

-hpa