Opteron Steppings . . .

A few people have taken one look at FX prices and then immediately started looking into the overclocking possibilities of lesser Opterons.

There’s a couple problems associated with that.

Upping the Multiplier

If you’re looking at overclocking a 1.4GHz Opteron, for all practical purposes, you’re going to need to up the multiplier.

The good news is upping the multiplier on an Opteron is probably doable, and it can be done through the BIOS. If you look here, you’ll see that one company managed the feat with an FX.

The bad news is nobody else has done this (at least publicly) yet with any BIOS modifications that will let you do so, though apparently one is expected fairly shortly.

What Stepping Is Your Hammer?

Increasing the multiplier is unlikely to be the big problem in overclocking a low-speed Opteron. Getting one capable of overclocking a lot will be.

From the AMD techdoc (page 6):

We can see that there’s been two Hammer steppings: the B3 stepping and the C0 stepping. We can also see that all Athlon64s and FXs are C0 stepping chips.

This also tells us how to distinguish the two using a program like CPU-Z or CPUID. A B3 stepping Opteron will read:

Family: F (or 15)
Model: 5
Stepping: 1

A C0 stepping Opteron will read:

Family: F (or 15)
Model: 5
Stepping: 8

That’s all very nice, but you can’t run CPU-Z on a chip in a tray.

Is there a way you can tell the difference just by looking at one?

Yes.

If you look at the first line of code on an old Opteron, you’ll see something like this:

OSA140CCO5AK

The codes we’re concerned about are in the middle. Do you see the “C-C-O”?

Those codes mean:

C = Socket 940
C = 1.55V
O = Maximum temp 69C

If you look at the codes of a newer Opteron, they’ll look like this

OSA140CEP5AK

See the “C-E-P”?

Those codes mean:

C = Socket 940
E = 1.50V
P = Maximum temp 70C

Every picture of a 64 or FX I’ve seen (which we know are all C0 steppings) have C-E-P in their code.. So do the pictures of 2.0GHz Opterons.

Every picture of the older Opterons have C-C-O.

It’s probably pretty safe to say that any Opteron with C-E-P is a C0 stepping, which any Opteron with a C-C-O is the B3 stepping.

Should you ever decide to try to overclock an Opteron, you definitely don’t want a C-C-O.

Per the second line of code, all fairly recent single processor Opteron/FX C-E-Ps so far seem to have “AAAIC” as the initial code on the second code line. Multiprocessor Opterons and Athlon64s seem to start with the letter “C”

If you see something like “AAAMC” that’s probably a little more advanced.

If anybody works for a place that sells low-end Opterons (i.e., 1.4 and 1.6), if it is at all possible and it’s not inconvenient nor will get you in trouble, could you look at what you have and see you have any of these C-E-Ps in those speeds?

It May Not Help, Yet

Even if you have the modified BIOS and you find yourself a 1.4GHz with a C-E-P designation sometime in the near future, it still may not do you any good.

That’s because we have no idea yet how well AMD is making these chips yet. We know they can make chips that can be sold as 2.2GHz chips. What we don’t know yet is whether those 2.2GHz are the cream of the crop, or close to typical.

You might get 2.4GHz, but you might get just 1.6GHz, too.

It’s called “being a pioneer,” and it will be an expensive adventure at that. A 140 Opteron, an Opteron mobo, and 1Gb of registered RAM looks like an $850 proposition at the moment.

The scary part is that if it did work, it would save you $500 over an FX system.

We don’t think it’s worth it, but, if you’re going to do it anyway, at least this should help a bit.

Ed