Problems with AMD64 and 8 GB RAM?

[Scott Long]

Greg 'groggy' Lehey wrote:
> 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.
> 

The SMAP will show the hole.  It's well documented in most PC 
archtitecure books.

Scott