A data input/output unit is provided. The data input/output unit which is connected to a processor, and receives and outputs data in sequence based on a first schedule includes a first input first output (FIFO) memory connected to an external unit and the processor; and a reordering buffer connected to one side of the FIFO memory, and store data outputted from, or inputted to, the FIFO memory in a plurality of buffer regions in sequence, and output data stored in one of the plurality of buffer regions based on a control signal provided from the processor.