Socket 940
Socket 940 is a 940-pin socket for 64-bit AMD Opteron server processors and AMD Athlon 64 FX consumer processors. This socket is entirely square in shape and pins are arranged in a grid with the exception of four key pins used to align the processor and the corners. AMD's Opteron and the older AMD Athlon 64 FX (FX-51) use Socket 940. Technical specifications. Microprocessors designed for this socket were intended to be used in a server platform, and as such provide additional features to provide additional robustness. One such feature is the acceptance of only  registered memory. While the more recent 940-pin socket AM2 is visually similar to this one, the two are electrically incompatible due to the integrated memory controller. Socket 940 CPUs integrate a DDR controller, whereas AM2 models use a DDR2 controller.