Re: how far could i oc this?
Socket 940 and AM2, have the same number of pins, but both their pins are placed differently. So no, they're not the same socket. Socket AM2 is the desktop line. And Socket 940, is for AMD's server line.
I'm not sure how far you can overclock the X2 4200+, on that kind of motherboard, as that chipset is not known for overclocking. But you should be able to overclock to 2.5-2.7...
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