I have an ASUS M3A78-EM motherboard with an AMD Phenom 9550 processor. I wanted to upgrade my RAM to 4GB. Will a 4GB DDR2 1066MHz RAM work on it? The manual says "Due to CPU limitation, DDR2 1066 is supported by AM2+ CPU for one DIMM per channel only". I don't know what this means and hence my doubt. I was thinking of either a Corsair or Kingston 2 x 2GB 1066MHz RAM.
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That means you can't use more than 2 1066 sticks and be stable, for example you can't use 4x1gb 1066mhz sticks and expect it to be stable( that's officially, it usually can be made stable with some tweaking).
With 2x2gb you'll be fine.
Alright.. Is there a big difference between 800 and 1066?