AMD uses various motherboard sockets for its 64-bit CPUs (Opteron, Athlon 64, Athlon 64 FX, Turion 64). Socket 940 (940 pins) supports dual channel memory controllers, and Socket 754 supports a single channel. Socket 939 was added later to provide a less-expensive motherboard option, one with only four layers rather than from six to nine. See AMD64.