A method is for operating a nonvolatile dual in-line memory module (NVDIMM). The NVDIMM includes a dynamic random access memory (DRAM) and a nonvolatile memory (NVM) device, the DRAM including a first input/output (I/O) port and a second I/O port, and the second I/O port connected to the NVM device. The method includes receiving an externally supplied command signal denoting a read/write command and a transfer mode, driving a multiplexer to select at least one of the first and second I/O ports according to the transfer mode of the command signal, and reading or writing data according to the read/write command of the command signal in at least one of the DRAM and NVM device using the at least one of the first and second I/O ports selected by driving the multiplexer.