text: its the amount if pins on the processor, thus a 754 wont fit into a 939 or visa versa.\n754 was the first mainstream amd64 socket. the max cpu that will be made for it is the 3700amd64. it is going to now be the budget line so it wont be developed a whole lot further as for as mainboard features. it does not feature dual channel memory.\nskt939 is the current enduser socket. processor speeds are going beyond dual core 4800+ processors so there is a definate upgrade path. it can handle dual channel memory. the motheboards have features like the nf4 chipset including SLI, pci-express, better sata options, and more. since better chips/chipsets are being manufactured on 939 it is also perferred for overclockers and \nThe major difference between S754 and S939 is that S939 processors have a 128-bit memory controller and the S754 has a 64-bit memory controller. In other words, dual-channel vs. single-channel. That's it, from the processor's standpoint. As for the other candy (SLI, PCI-E, etc), those are generally to be found on S939 motherboards, simply because those are where the manufacturers make their money.