A display device (2) can be coupled to or independent from a host computer (1). When coupled to the host computer, the display device serves as a man-machine interface of the host computer. The display device includes an external operation unit (80), a display unit (20); a memory (60); and a processing unit (50). The external operation unit is provided to produce operational commands corresponding to operational inputs. The processing unit is for receiving data files from the host computer and storing the data files in the memory when the display device is coupled to the host computer, and for reading the data files from the memory and displaying the data files on the displaying unit in accordance with the operational commands when the display device is independent from the host computer.