It's physically and electrically compatible with all socket A motherboards, but if the motherboard BIOS doesn't have the voltage and multiplier map for the CPUID value, then the board will "test" and accept the lowest settings the CPU, unaware that the multiplier and voltage can be altered on the fly, and leaving it set at it's lowest settings. I know, but were there really NO exceptions, I mean no mobile axp cpu's with different sockets?