AM2+ Backwards Compatibility and the AM3 socket
As mentioned earlier, the Phenom II X4 processors still make use of the AM2+ socket, the very same socket used by existing Phenom X4 and X3 processors.
Motherboard makers such as Asus and Gigabyte have already released a first round of BIOS updates enabling their current AM2+ motherboards to support the new Phenom II X4 processors.
We like to believe this is the perfect upgrade path as those who invested in a Phenom platform a year ago need only to purchase a newer more powerful processor to upgrade. This also allows those looking to build a new Phenom II X4 computer to choose from a huge range of mature AM2+ motherboards. The groundbreaking 790GX chipset also supports the Phenom II X4, offering enhanced tuning via its advanced clock calibration feature.
Another interesting upgrade opportunity for AMD users will be the upcoming AM3 socket, said to become available some time in February. The AM3 socket will be used with future AMD desktop processors. AMD has confirmed that AM3 processors will work on some AM2+ motherboards, while AM2/2+ processors will unfortunately not work on the newer platform. This is because of the lack of the DDR3 memory controller.
Furthermore the AM3 socket will have two less pins (938), making it mechanically incompatible with older 940-pin AM2/2+ processors.
Unlike the LGA1336 (Core i7) socket, the AM3 socket will be capable of running either DDR2 or DDR3 memory, but not both on the same motherboard. At least today that sounds like an excellent option to have given DDR3's pricing compared to DDR2.