A data mask system includes a processor providing control signals including a command signal, an address signal, and a data signal, a data mask processor receiving the control signals and providing either write data or masked data in response to the control signals, and generating data mask information and a data mask selection signal from at least one of the control signals, and a data mask register unit receiving the data mask selection signal, storing the data mask information, selecting a subset of the stored data mask information in response to the data mask selection signal, and returning selected data mask information to the data mask processor. The data mask processor receives the selected data mask information from the data mask register unit and provides the masked data as a result of performing a data mask operation on the data signal according to the selected data mask information.