I hope I'm not being redundant here. I did a search and still can't find the answer I need. I am upgrading the mother board. I have three sticks DDR2 677. The mother board says its standard is DDR2 1066. So, can I use the slower memory on the faster mobo? I am guessing I can and it will just clock down to the 677 but i want to make sure. How does the CPU come into play? If I want to upgrade to 1066, do I have to make sure my CPU can handle it? Is it worth it to upgrade from 667 to 1066? With the same amount of RAM, how much of a performance increase am I looking at? Thanks

AMD system or Intel? Just because the board supports up to DDR2-1066, it doesn't mean it's required...it depends more on the CPU. With *most* AMD systems, you should use DDR2-800 for best performance. The A64 & X2 do not offically support DDR2-1066 & will underclock it to DDR2-800 if it's installed. The X3 & X4 will perform best with DD2-1066 though. You can run any of them with DDR2-667 if you're willing to take the performance hit. If you're building an Intel system, it would depend on the CPU / FSB. AFAIK, there is no Intel CPU that *requires* DDR2-1066. 800MHz FSB CPUs should be run with DDR2-400, 1066MHz FSB CPUs with DDR2-533, 1333MHz FSB CPUs with DDR2-667, 1600MHz FSB CPUs with DDR2-800. In any of these cases, you can use higher rated RAM & simply underclock it to the optimal speed.

Thanks for the fast response!