Abstract: A memory module for expanding memory of a computer. The memory module comprises a printed circuit board including a connector edge having a plurality of contact pads configured to convey data signals, power and ground to and from said printed circuit board. The power and ground contact pads alternate along said connector edge with no more than four adjacent data signal contact pads without intervening power or ground contact pads. A plurality of memory devices mounted on the printed circuit board. A clock driver is coupled to each of the plurality of memory devices and is configured to receive a differential clock signal and to produce at least one single-ended clock signal for clocking the plurality of memory devices. The clock driver includes a phase-locked loop for phase-locking the at least one single-ended clock signal.