A method includes: providing a DDR interface between a host memory controller and a memory module; and providing a message interface between the host memory controller and the memory module. The memory module includes a non-volatile memory and a DRAM configured as a DRAM cache of the non-volatile memory. Data stored in the non-volatile memory of the memory module is asynchronously accessible by a non-volatile memory controller of the memory module, and data stored in the DRAM cache is directly and synchronously accessible by the host memory controller.