Problems with AMD64 and 8 GB RAM?

[Greg 'groggy' Lehey]

On Wednesday, 30 March 2005 at 16:01:14 -0700, Scott Long wrote:
> 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 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, and I'm going to make this an FAQ and post it in a very obvious
> place, since 4+ GB is so easy to get and people don't seem to understand
> the PC architecture very well.

That's not easy to understand when it's barely documented.  Thanks for
the info: it helps a lot.

This may still be a hint, though: that memory hole doesn't show up
during a boot with 8 GB RAM.  How come?  Is the system trying to map
RAM over the PCI hole?

It looks as if I should get a verbose boot listing with 8 GB.  It'll
be a couple of hours before I find time to reboot this machine.  In
the meantime, there's a verbose boot with 4 GB at
http://www.lemis.com/grog/Images/20050331/obelix-dmesg.  I'm told it
shows a number of strange things, including incorrect reporting of
on-chip cache sizes.

Greg
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