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OK I have a motherboard which supports DDR3 memory. Currently I have 2 * PC3-10666 2GB in it (4GB total). I plan to remove them and replace them with 4 * PC3-12800 2GB (8GB total).

My motherboard supports:

4 x DIMM, Max. 8 GB, DDR3 1600*/1333/800 Non-ECC,Un-buffered Memory Dual channel memory architecture

*Overclock speed

Can I safely assume that my new PC3-12800 DIMMs will work with my motherboard (which uses PC3-10666 currently)?

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I'm pretty sure RAM will under clock if I'm not mistaken. I vaguely remember getting RAM for and old server RMA'd and they sent faster RAM and it was fine since the MB just under clocked it to match the bus. And this was ECC, etc, etc. –  skub Jan 20 '12 at 19:57
    
In fact I don't think it will underclock in my case since my current ones works at 1333 and my new one will work at 1600 (which my mobo supports) but yes I get the idea that faster ones will work OK but at "slower" speed (like a USB 3 drive in a USB 2 port). –  AlexV Jan 20 '12 at 20:07
    
@AlexV If you know that your MB will support your PC3-12600 ram at 1600 (and you are right), what is the question you're asking here again? You can check your MB's QVL to see if they tested your specific brand, or see what comes up of some googling for your MB + ram models, but other than that if it matches the technical specs, it will work unless there's an unexpected compability issue you cannot otherwise predict. –  mtone Jan 20 '12 at 21:54
    
@mtone My motherboard manual only states that it supports DDR3 1600*/1333/800 it's not talking about any PC3-... And unfortunately the QVL is 5 years old. I was just not sure about all there PC3- I tought maybe there were different DDR3 kind of DIMMs, –  AlexV Jan 23 '12 at 14:48
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Nope, PC3 = DDR3. You just have to match the PC3 number to the DDR3 frequencies. See en.wikipedia.org/wiki/DDR3_SDRAM#JEDEC_standard_modules. You should get either 12800 (1600) or 10666 (1333). The performance difference is marginal in most cases. –  mtone Jan 23 '12 at 19:15
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1 Answer

up vote 1 down vote accepted

The motherboard specification says it will take 1600 if you overclock. So yes, you can use PC3-12800, since that has a 800 mhz bus speed. The Asus BIOS should over clock it on first boot automatically.

It's been a while since I've purchased RAM; it didn't click that PC3-12800 is an 800 mhz bus with a 1600 data rate.

tl;dr = PC3-12800 is 1600 data rate.

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I love the two points for the comment above, and then the -2 for the answer that just elaborates the same facts. –  skub Jan 20 '12 at 23:17
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