Socket AM3 versions of the Phenom II are backwards-compatible with Socket AM2+, though this is contingent on motherboard manufacturers supplying BIOS updates. In addition to the Phenom II's pin compatibility, the AM3 memory controller supports both DDR2 and DDR3 memory (up to DDR2-1066 and DDR3-1333), allowing existing AM2+ users to upgrade their CPU without changing the motherboard or memory. However, similar to the way the original Phenom handled DDR2-1066, current Phenom II platforms limit the usage of DDR3-1333 to one DIMM per channel; otherwise, the DIMMs are underclocked to DDR3-1066. AMD claims that this behavior is due to the BIOS, not the memory controller, and plans to address it with a BIOS update. The dual-spec memory controller also gives motherboard manufacturers and system builders the option of pairing AM3 with DDR2 to reduce overall system cost, as compared to competing chips from Intel, which require DDR3.