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I have a server that came with two sticks of 2GB PC2-6400 ECC ram (Hyundai). We also bought two sticks of Corsair CM2x2048-6400C5C (PC2-6400). So I installed all 4 sticks and the machine started beeping and wouldn't boot. So I took out the factory RAM and tried just the Corsair RAM and it booted fine. Took that out and tried the factory RAM and it booted fine.

So I was super confused and then read about mixing ECC sticks from this post. I then thought I'd consult the technical manual of the system board. The odd thing is that it states it requires unbuffered RAM to work. There's no real indication to me that the modules can't be mixed.

Could someone try to explain what the problem could be?

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Are you sure they are both unbuffered or are they both registered? – xxl3ww Sep 2 '10 at 13:22
It's not clear from your post, so please note that ECC and buffered / registered RAM are not the same thing. A stick can be none, one or both of them. – DMA57361 Sep 2 '10 at 13:25
99% sure it is unbuffered. Registered memory is keyed differently. – hanleyp Sep 14 '10 at 16:08
up vote 1 down vote accepted

From the question you have linked to the general feeling is that mixing ECC/non-ECC RAM may or may not work, dependant on the motherboard / chipset and maybe the RAM as well.

The data sheet for the Primergy TX100 S1 (which I assume is what we're looking at given the document you link to) clearly states ECC support, but gives no mention of this particular issue. However, it does tell us it uses an Intel 3200 chipset. But, looking up this doesn't provide any answers either.

I'm inclined to say that your motherboard wants to run all the memory either with or without ECC, and cannot handle running some with and some without.

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According to the Intel 3200 chipset datasheet, section 1.2.2, the chipset does not support mixed ECC and non-ECC configurations.

Supports both un-buffered ECC and non-ECC DDR2 DIMMs. The MCH does not support memory configurations that mix ECC and non-ECC un-buffered

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