The Copper Silent 2M is basically identical to the Copper Silent 2, however it utilizes the following additional feature:

3 Selectable Rotation Speeds
In order to reach the exact cooling that your CPU needs, 3 speeds can be selected via a switch. This switch has been attached to a metal bracket and can be installed in any PCI slot. Further an additional control can still be installed. In this case the three fan speed selections mark only the maximum rotation speed.