The nm stands for nanometer - the distance used to measure the die shrink on the core of the CPU. Essentially, the smaller the die shrink, the less heat created; therefore, resulting in better performance and OCability. Also, this makes the CPU's cheaper to make. As long is the CPU is the correct socket, it will fit in a compatible mobo. For instance, a Socket 939 90nm Winchester core A64 will fit in the same board that a 130nm Newcastle core A64 will fit in. Hope this helps.