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GA-MAa78GM-S2H and TWIN2X2048-6400C4 & TWIN2X4096-6400C5


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I've only just built my system.


The first memory I bought was the 2GB pair. One stick works in all the memory slots. The other works in none. The system doesn't even complete POST. And as a pair they don't POST either.


Presuming I had one faulty memory stick I ordered the 4GB pair. One stick get half-way through boot but then freezes. If booted in safe mode it works. The other stick (or as a pair) will not complete POST.


Am I missing something really obvious here?!


Though not a dedicated IT professional I have built PC's before and upgraded memory on many occasions.

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Well, I've got the 4GB kit working in slots 3&4. So I now have 4GB of RAM and the system is flying quite nicely.


HOWEVER, I'd still like to get to the bottom of this. Having tried all the RAM in every slot individually this is what I found:


..................2GB #1 2GB #2 1GB #1 1GB #2

Channel 0, DDR2-1 ...h... ..h... ..y... ..n

Channel 1, DDR2-2 ...n... ..n... ..y... ..n

Channel 0, DDR2-3 ...y... ..y... ..y... ..n

Channel 1, DDR2-4 ...y... ..y... ..y... ..n


y = works

n = doesn't work

h = works in safe mode but in normal mode can't freezes half way through windows boot.


Sorry the formatting's not brill.


As you can see from the table above, the only possible pair I could put in was the 4GB set.


What would be the likely causes of this? Is it the motherboard? the RAM? the BIOS? or something else, maybe? Any ideas how I can find out for sure?


Your thoughts would be appreciated. I dont want to come to upgrade it in a few years time and find that there's something I should have fixed now.


PS - I'm returning the 2GB kit, as planned, to the company I purchased them from.

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  • Corsair Employees
I would not suggest mixing memory on any MB as you have found it does not work that well. And if you do install more then two modules DDR667 would be suggested. And set the memory Voltage to 2.0 Volts and set the NB/MCH Voltage to +.2 Volts.
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Thanks for your reply and advice.


I never actually tried it with mixed memory. I tested each stick on its own, in every slot, with no other RAM installed.


I'm baffled why one memory stick works in some slots and not others, while another will work in every slot. I'd understand it if it was consistent, but its not. I would expect RAM to work (or not) in every slot when installed at normal voltages and speeds.


What is the most likely cause of this?


Also, what difference does the memory speed make? If I wanted to upgrade in the future I would be looking to go for faster, not slower, memory. The motherboard (with a phenom CPU) supports 1060! Why do you reccomend 667 over the higher speeds?


Thanks for your help. I'm finding this very confusing indeed.

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  • Corsair Employees

With that platform/Mother Board I would suggest that all of the modules match and if you switch from one to another you may have to reset the MB BIOS before it will see the other modules properly.


I would suggest replacing what you have now with one set of Twin2x4096-8500C5DF if you weant 4 gig of faster memory.

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