Re: Problems with AMD64 and 8 GB RAM?

From: Greg 'groggy' Lehey (grog_at_FreeBSD.org)
Date: 03/31/05

  • Next message: Jon Noack: "Re: new LORs on 5.4 pre" 
    Date: Thu, 31 Mar 2005 08:45:41 +0930
To: Scott Long <scottl@samsco.org>

    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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