Problems with AMD64 and 8 GB RAM?

David O'Brien obrien at
Thu Mar 31 10:47:33 PST 2005

On Thu, Mar 31, 2005 at 08:14:45AM +0930, Greg 'groggy' Lehey wrote:
> > 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.

No.  This is due to the 3.5-4.0GB PA address range that the PeeCee
architecture reserves for the PCI config space, AGP GART, memory mapped
I/O, etc...  Many Opteron BIOS's don't bother to hoist the "covered"
memory above 4GB.

Please see the freebsd-amd64 archives -- this has been discussed many

-- David  (obrien at

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