A high density high reliability memory module with power gating and a fault tolerant address and command bus. The memory module includes a rectangular printed circuit board having a first side and a second side, a length of between 149 and 153 millimeters and first and second ends having a width smaller than said length. The memory module also includes a first plurality of connector locations on the first side extending along a first edge of said board that extends the length of the board and a second plurality of connector locations on the second side extending on said first edge of said board. The memory module further includes a buffer device in communication with the circuit board for accessing up to four ranks of memory devices mounted on the first side and second side of the circuit board. In addition, a power savings means is included for causing all or a portion of the buffer device to be in an inactive mode in response to current activity at the memory module. The memory module also includes a locating key having its center positioned on said first edge and located between 82 mm and 86 mm from said first end of said card and located between 66 and 70 mm from said second end of said card.