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Is it safe using RAMs with different Frequencies

I'd like to use 2 x 4GB DDR3 1600 dimms in a motherboard capable of only DDR3 1066. The DDR3 1600 is on sale and the cost is identical to 1066 dimms. It'd be nice to have these faster sticks around should i upgrade the motherboard. I assume the RAM can under clock itself or be changed in the BIOS.

While obviously it's less than ideal situation, I don't know if there are other unintended consequences in terms of stability, performance and longevity of the board and said RAM. Am I doing any damage to the memory controller or RAM?

I've always bought RAM at the max speed specified for the motherboard and I've never gone over so I'm not sure if there any caveats to this at all.

Edit: I intend to use the RAM in pairs. I know that mixing RAM speeds is just a bad idea.

marked as duplicate by Sathyajith Bhat Nov 24 '11 at 2:40

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There are two possible negative consequences.

  1. System will run at the speed of the slowest RAM
  2. System will not boot

If the second happens, just take it out, or see if you can manually underclock it.

Unless you put in the wrong type of RAM, or put it in backwards or something, no damage will be caused.

See here for more information.

  • If the disparity between the two speeds is large enough (1600 to 1066 for example), does the likelihood of booting decrease? – osij2is Nov 24 '11 at 0:55
  • 1
    I don't see that discussed anywhere, so I'm not sure, but I would tend to doubt it. The only reason that there would be an issue would be that the RAM cannot be underclock to the lower speed, not something that will happen in your case (I believe, but I've never heard of it happening). – soandos Nov 24 '11 at 0:59
  • Yeah, I've never heard of it too so I'm a bit leery of trying this out only to find that it won't work. Thanks for your input! – osij2is Nov 24 '11 at 1:01

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