"Only few months after presentation of Phenom II X4 940 Black Edition and Dragon platform, AMD made its next move: transition to a new memory standard - DDR3. New standard, as it is in most cases, demands new socket. In this case pin configuration isn't too much different from the one present on AM2+socket, but there are differences because of which it is not possible to insert old AM2 CPU into new AM3 motherboard. As you probably know, AM3 CPUs, among which is new X4 955, are AM2/AM2+ compatible so you can use them on alder motherboards that are compatible with older DDR2 memory standard. AMD this time made a smoother transition to new memory standard without danger of losing market share."