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Date: Wed, 30 Mar 2005 14:57:15 -0800
From: Steve Kargl <sgk@troutmask.apl.washington.edu>
To: "Greg 'groggy' Lehey" <grog@FreeBSD.org>
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cc: FreeBSD Stable Users <freebsd-stable@FreeBSD.org>
cc: FreeBSD-amd64@FreeBSD.org
Subject: Re: Problems with AMD64 and 8 GB RAM?
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On Thu, Mar 31, 2005 at 08:14:45AM +0930, Greg 'groggy' Lehey wrote:
> On Wednesday, 30 March 2005 at 14:35:46 -0800, Steve Kargl wrote:
> > On Thu, Mar 31, 2005 at 07:54:39AM +0930, Greg 'groggy' Lehey wrote:
> >> None of these problems occur when I use 4 GB memory.  About the only
> >> strangeness, which seems to come from the BIOS, is that it recognizes
> >> only 3.5 GB.  If I put all DIMMS in, it recognizes the full 8 GB
> >> memory.
> >>
> >> I realize that this isn't enough to diagnose the problem.  The reason
> >> for this message now is to ask:
> >>
> >> 3.  Where should I look next?
> >
> > Have you run sysutils/memtest86 with the 8 GB?
> 
> Heh.  Difficult when the system doesn't run.

That's what happens when 1 of 8 (1 of 4?) DIMM is bad :-)

> > I had 4 bad out of 12 tested where the DIMMs were Crucial PC2700 2GB
> > Reg. ECC DIMMs.
> 
> OK, this makes sense.  It might also explain why the 4 GB
> configuration only recognizes 3.5 GB.

Search amd64 mailing list.  The missing memory is reserved for
something which escapes me at the moment.  Similar to the 
infamous ISA memory hole.

-- 
Steve