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Missed the 3gb, thanks.

What type. Does it have to be 667 MHz or can it be 800? What is the difference?
Thanks

I believe you have to get the 667 MHz.

As for brands, if you can find Crucial or Corsair that's what most people on this site buy. Amazon runs some good deals for newer kinds (some older ones are hard to find these days) but it's a good place to start.
 
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