1. A memory module comprising: a module substrate; and a plurality of memory chips mounted on said module substrate and respectively having a plurality of chip data terminals, wherein said module substrate has a plurality of module data terminal pairs individually provided in association with the respective chip data terminals included in said plurality of memory chips, and a plurality of module data wirings which respectively connect between said plurality of module data terminal pairs, and said plurality of module data wirings are connected to their corresponding chip data terminals and available as a memory access data bus.