A memory module includes a first printed circuit board (PCB) which includes a first surface, a second surface, first taps formed on the first surface, and second taps formed on the second surface, a first buffer attached to the first PCB, and first memory devices attached to the first PCB, in which the first buffer is configured to transmit signals input through the first taps and the second taps to the first memory devices, and signals re-driven by the first buffer among the signals are transmitted to a second module through the second taps.