Memory module and memory system

A memory module comprising:

• a plurality of semiconductor dies connected with an external device through a common channel, the plurality of semiconductor dies configured to operate in response to control signals from the external device, wherein
• the plurality of semiconductor dies form ranks a number of which is not a power of two, and
• semiconductor dies of the plurality of semiconductor dies in a same rank receive a chip selection signal in common and semiconductor dies in different ranks receive different chip selection signals.

A memory module comprising:

• sets of semiconductor dies arranged in ranks on a printed circuit board, each set of semiconductor dies in a same rank configured to communicate with a controller over a common channel and a number of the ranks arranged on the printed circuit board not being a power of two, wherein
• the number of the ranks arranged on the printed circuit board corresponds to one of three, five, six, and seven.