Re: PAE and PSE ??

Rafael J. Wysocki
2006-10-23T14:14:33Z

On Monday, 23 October 2006 16:10, H. Peter Anvin wrote:
> 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.

Agreed.