Subject: Re: NetBSD 1.6.1 not finding all memory
To: D'Arcy J.M. Cain <darcy@NetBSD.org>
From: Allen Briggs <email@example.com>
Date: 12/24/2003 10:40:29
On Wed, Dec 24, 2003 at 07:37:11AM -0500, D'Arcy J.M. Cain wrote:
> I have been trying to find information about PSE36 and what I have found is a
> little sketchy. However, it appears that PSE36 is a hack for systems that
> use 32 bit pointers. Don't we use 64 bit addressing? Shouldn't we be seeing
> all of this memory without turning it into a RAMDrive or something?
We use 32-bit addressing on 32-bit systems, and ia32 is a 32-bit system.
Some ia32 chips have an extension that allows them to address up to 36
bits-worth of physical address, but only 32 bits at a time. This is
done, I think, by extending the page table to allow for specifying a
36-bit physical address in the page table. So each process (well, each
address space) is limited to 4GB with 32-bit pointers, but the system
itself will be able to address up to a total of 64GB or whatever, spread
between different processes.
But I think I've heard it called PAE or Physical Address Extensions or
some such, not PSE36.
At least, that's my paltry understanding from what I've picked up here
and there. I don't claim to understand ia32... :-)
Allen Briggs firstname.lastname@example.org
Wasabi Systems, Inc. http://www.wasabisystems.com/