VERY peculiar memory behaviour across DIMM slots

I just ran a quick test with my DFI nForce4 board, and am totally surprised by the results.

First off, I have noticed that when my memory is overclocked to the point where it starts to cause errors, it always causes errors at the same adresses.

Intrigued, I tried switching the two sticks between RAM slots. Stick one was in slot one, stick two was in slot three - I moved stick one to slot three, and stick two to slot one.

Strangely enough, the errors still occured at the same memory adresses.

But even more peculiar, I found that with the sticks set up one way in the same two slots, they produced more errors than they did when set up the other way in the same two slots.

With stick one in slot one, and stick two in slot three, I averaged ~5.2 errors per pass of memtest86 test #5. With stick one in slot three, and stick two in slot one, I got several hundred errors per pass. I immediately switched them back, and got my ~5 errors per pass again. I switched them back and forth twice to make absolutely sure - the difference in stability (as measured by the number of errors per pass) is signifigant and reproduceable 100% of the time.



What on earth is going on here? Why do my memory sticks appear to "prefer" one slot over the other, of the same pair of slots?

Could some of you please try exactly what I just outlined above, and see if your results line up with mine? You'll need an unstable memory overclock in order to count the errors, and "measure" stability.

This is too weird.

O.K., I just finished quickly testing the same thing, but with the other two memory slots on my board (1 and 3 are the yellow slots on this board, 2 and 4 are the Orange slots).

The exact same behaviour occurs with the Orange slots. The difference is smaller, but still present with stick one in slot two, and stick two in slot four, I got about 9 errors per pass of test #5 (I stuck to 15 loops of test #5). With stick one in slot four, and stick two in slot two, I didn't get any errors at all after ten loops of test #5! I tested the Orange slots twice as well - the difference is reproduceable and consistant. My previous testing of the slots had the Yellows giving me better stability, but with rearranged sticks the Oranges appear to actually be better.

I must stress that the same two memory slots were used.

Forgive me if it seems like I'm making a big deal about nothing, but I am astonished and amazed at this. With the same two slots, the memory behaves drastically different depending on which stick is in which slot. I can't believe I've stumbled across this. What the heck is going on with this?

If anyone can spend 15 minutes to test their board out in a similar manner I would appreciate it. This can't be just my board, not with both sets of memory slots behaving like this. For all we know, this has been holding back potential memory overclockability for any number of of people.


If anyone has an explanation or speculation, please share it. I am dumbfounded.

yup youll see some wierdness with the SD. with my old kingston bh-5, memtest is ok yellow or orange, however, i cant break ~235'ish in orange while in windows stress testing. yellow can exceed that.

with ocz gold 3200 (UTT BH), yellow or orange memtest ok, but windows stress, yellow cant exceed ~240, so orange must be used.

with my prior winnie, the memory (KHX) liked it better in orange then yellow.

Mate,

These peculiarities have been witnessed by many. So rest assured, your board is not funky . With this board, certain memory chips prefer certain slots. Very weird but true. Also, while you are at it, could you measure the Vdimm with a multimeter through each slot? I think it is pin 7 on the DIMM slot, but you should double check this.

I won't be surprised if you find that the Yellow ones read different from the Orange. The orange ones are the designated TCCD slots (unofficially ofcourse) and the yellow ones BH-5. However, as I am finding out for myself, the Orange slots offer better stability than the yellow ones. With the same TCCD and timings, I get about 2 errors per pass on memtest#8 in the yellow slots. The orange slots yeild zero errors @DDR600.

Yes, I can confirm memory erroring out at the same spot even when sticks are switched ! I would offer a few reasons off the top of my head (mere speculation, may not stand detailed scrutiny):-

-The 5V line feed to the DIMM's are not O.K. But neither is the 3.3V (since I'm not using the 5V line), hence you see this discrepancy. Can be confirmed by VDimm measurement.

-Cheapo DIMM slots (notice that they seem to move a bit more than usual).

-This could be a BIOS problem. I absolutely rule out the CPU because I saw the exact same problem with my 3500+ Newcastle.

You may also find out that switching slots would entail change in timings! If that is the case, we have a serious problem becasue it would mean the electrical paths on the board are not of the same length and the signals are out of phase (blame the phase locked loop).

I have found ion several occasions that if I reverse my ram slots that I will get more errors. I believe, whether it's true or not I don't know, that the ram just gets burned into a certain slot and does not respond well to being reversed. Maybe ram doesn't like change any more than people do.

Cool, I guess I'm not alone, nor the first to notice this

I'll check the VDIMM at both slots, and see if there is any discrepency at all between them. In particular I am also wondering about timings, and whether they'll change between slots or not. I certainly hope not.

Sigh, it just means a lot more testing to do.

rseven,

I don't know of a mechanism which causes the RAM to like one slot more than the other . Since I did not test for this right off the bat (with brand new RAM), there is no way to say if a burn in contributes to this. Let me reiterate that this has NEVER happened on my ASUS A8V. Looks like DFI have some issues ?