Subject: Re: dmesg From PowerEdge 8450
To: Thomas T. Thai <>
From: Martin Husemann <>
List: tech-smp
Date: 03/21/2004 12:35:25
On Sun, Mar 21, 2004 at 05:21:05AM -0600, Thomas T. Thai wrote:

> Could someone explain about the 4 Gig RAM limit?

The i386 architecture is a 32 bit processor, which means (besides others)
that pointers are 32bit wide. You can only address 4 GB linearily with a
32 bit pointer.

When this started to become a limit, the architecture grew a hack:

> cpu0: features 383fbff<PGE,MCA,CMOV,PAT,PSE36,MMX>

The Page Segement Extensions (IIRC) allow the mapping of a 36 bit wide
physical address range into the virtual 32bit addresss range.

There is no support for using this extension in NetBSD yet (and I have
zero clue how intrusive that would be)