High performance, high capacity memory modules and systems

Described are memory modules that include address-buffer components and data-buffer components that together support wide- and narrow-data modes. The address-buffer component manages communication between a memory controller and two sets of memory components. In the wide-data mode, the address-buffer enables memory components in each set and instructs the data-buffer components to communicate full-width read and write data by combining data from or to from both sets for each memory access. In the narrow-data mode, the address-buffer enables memory components in just one of the two sets and instructs the data-buffer components to half-width read and write data with one set per memory access.