The invention provides a memory device including a memory array, an internal memory, and a processor. The memory array stores node mapping tables for access data in the memory array. The internal memory includes a namespace table and an index table The processor obtains a data access command from a host device to determine whether a data of the data access command contains one of the NSIDs, assigns the at least one internal NSID to the data of the data access command according to the data access command in response to the data of the data access command that does not contain the namespace identifier, and, the processor manages the data with the internal NSID by the namespace table and the index table.