Opteron Vs. Athlon X2

[Mark Hahn]

> So what does "without" mean?  That only 4GB is not allowed with ECC?
> Or that ECC doesn't work at all.  Or that it works but you don't
> actually get the error correction?

my understanding is that unbuffered ECC dimms simply provide 72b wide
storage rather than 64.  if the bios doesn't configure the k8's memory
controller to do the ECC dance, the bits just evaporate (or maybe they
all get pulled high/low.)  putting 64/72 in the dimms SPD would make sense.

> I've seen wording in amd64 manuals (of the older generation) that
> I read to mean that the dimms would work (the CPU would be able
> to read/write to memory) but not provide ECC.  

I suspect that ECC works in all K8's, but that the bios leaves ECC 
unconfigured if it sees, say, a sempron CPUID.  even the s754 pinout 
DOES contain the memcheck[7:0] bits for ECC, though.  AMD might
leave those pins unconnected, but I suspect they wouldn't bother.

> Things seemed really murky for the athlon, athlon XP, and earlier
> AMD64 motherboards I looked at.  I was glad that the opteron was

the big change is onboard memory controller, and so the question is 
where the different model become distinct - die, packaging, cpuid?
if I were AMD, I'd just flash/etch the CPUID right before shipping,
and expect the bios to respect my product positioning...

regards, mark hahn.