Problems with AMD64 and 8 GB RAM? (solved)

[Greg 'groggy' Lehey]

On Thursday, 31 March 2005 at 10:59:02 -0800, David O'Brien wrote:
> On Thu, Mar 31, 2005 at 11:24:29AM +0930, Greg 'groggy' Lehey wrote:
>> On Thursday, 31 March 2005 at 10:32:33 +0930, Daniel O'Connor wrote:
>>> On Thu, 31 Mar 2005 08:14, Greg 'groggy' Lehey wrote:
>>>>> Have you run sysutils/memtest86 with the 8 GB?
>>>>
>>>> Heh.  Difficult when the system doesn't run.
>>>
>>> You could try http://www.memtest86.com although that doesn't do >4Gb
>> :(
>>
>> I'm pretty sure it's not the memory.  I've tried each pair
>> individually, and it's only when they're both in there together that
>> it's a problem.  And yes, I've tried them in each pair of slots.
>
> You have a dual-channel memory controller.  If you insert one DIMM you
> perform 64-bit data accesses.  If you install DIMM's in pairs (making
> sure you're using the right "paired" sockets), you perform 128-bit data
> accesses.  Thus your access pattern is different between these two
> situations.  I'm highly suspious that you can us 4x2GB DIMM's with out
> knowing the exact part number.  Don't forget 2GB DIMM's are
> double-stacked and thus look like double the electrical bus loads.  The
> same is true for older 1GB DIMM's.

This looks like it's the issue.

> Install all the memory you would like to use into your motherboard,
> download memtest86+ version 1.40 from http://www.memtest.org, dd to
> floppy or burn the ISO, and report back your findings from running
> it.

Done that.  It was quite revealing.  This particular motherboard and
BIOS supply either "ECC off" or "ECC in chip kill mode".  Mine was
off, and I got many errors.  With 4 GB (any two chips) and chip kill
mode enabled, I ran memtest86+ for about 18 hours and got about 1 ECC
error per second.  With 8 GB, with or without chip kill, neither
FreeBSD, memtest86+ nor Linux run reliably: memtest86+ spontaneously
reboots every 5 minutes or so.

I borrowed this memory to test the motherboard, and it's going back
this week anyway.  I now have my own memory :-(all 1 GB of it), and it
tests perfectly.  The memory I had the trouble with works perfectly in
the machine for which it was purchased, so it does indeed look like an
electrical loading problem.

The moral of the story is, I suppose, "don't buy the MSI K8T
Master2-FAR".  I was warned about the motherboard before I bought it,
but at the time it was the only game in town.  Now I know of other
places with (hopefully) better boards.

Greg
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