A semiconductor memory device is configured to input a mode set code and set data on-the-fly in response to a mode set command, process data bit number information a write command to generate a first data signal, process data bit number information with a read command to generate a second data signal in response to the data on-the-fly indicating an enabled state, access a selected memory cell based on a word line selection signal generated using a row address and active command and a column selection signal generated using a column address and write command or read command, process a first quantity of data bits and transmit the first quantity of data bits to the selected memory cell in response to the first data signal, and process data received from the selected memory cell and output a second quantity of data bits in response to the second data signal.