Subject: Re: 4MB pages?
To: None <>
From: Bill Sommerfeld <>
List: tech-kern
Date: 09/06/2000 13:33:39
> Don't the PAE on the x86 support both 2MB and 4MB pages, at least in Intel's
> implementation?

The intel feature bits are:
	PSE		4mb page
	PAE		36 bit physical addresses
	PSE36		36 bit PA / 2mb page.

You get 4K/4MB pages with 32 bit PA's and 32 bit PTE's		(PSE)
You get 4K/2MB pages with 36 bit PA's and 64 bit PTE's		(PAE, PSE36)

You can't simultaneously have 2mb and 4mb pages; you can only get 2mb
pages if you use the large PTE format.

Large pages are selected by a bit in the page directory (2nd level
page table page) indicating that the PDE points to a large page rather
than to a page table page.   

When PAE is turned on, each PTP holds 512 PTE's rather than 1024, so
it maps 2MB rather than 4MB of VA space.

						- Bill