Subject: Re: NetBSD 1.6.1 not finding all memory
To: D'Arcy J.M. Cain <>
From: Allen Briggs <>
List: tech-kern
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           
 Wasabi Systems, Inc.