Abstract: In a computer system to which externally- and internally-set hard disk drives can be coupled, a drive number is set to the externally-set hard disk drive and/or internally-set hard disk drive in accordance with a coupling state of the externally- and internally-set hard disk drives and a swithing state of a dip switch of the externally-set hard disk drive. When the externally-set hard disk drive and/or internally-set hard disk drive are/is coupled to the computer system, pop-up menu data for the externally-set hard disk drive and/or internally-set hard disk drive is added to the normal pop-up menu data. A pop-up menu is therefore displayed using the normal pop-up menu data including the pop-up menu data for the externally-set hard disk drive and/or internally-set hard disk drive.

Abstract: When a computer is not externally powered, it operates from installed first and second batteries. In top surface of the computer, LEDs are provided which indicates three states of each battery; need of charging, during charging, and completion of charging.

Abstract: A boot process is performed from one of a floppy disk drive, a detachable hard disk drive, and a DOS-ROM. The boot priority is changed in accordance with the connection state of the detachable hard disk drive. The boot priority can be changed quickly by depressing a function key from a normal boot mode to an HDD boot mode or vice versa.

Abstract: A battery operable personal computer comprises a display, a keyboard, a CPU, and a power supply circuit. The display panel displays various types of data at a luminance level according to a value of a luminance control signal. The keyboard serves to enter data instructing alteration of the luminance level of the display unit. The CPU instructs the luminance level of the display unit in accordance with data entered through the keyboard, The power supply circuit controls the value of the luminance control signal to be supplied to the display unit in such a way that the luminance level of the display becomes one specified by the CPU.

Abstract: A boot process is performed from one of a floppy disk drive, a detachable hard disk drive, and a DOS-ROM. The boot priority is changed in accordance with the connection state of the detachable hard disk drive. The boot priority can be changed quickly by depressing a function key from a normal boot mode to an HDD boot mode or vice versa.

Abstract: A computer includes a key input unit having both cursor keys and a mouse mechanism, a keyboard having a holding section for detachably holding the key input unit, and a connector which electrically connects the key input unit and the keyboard together when the key input unit is held in the holding section of the keyboard. The computer further includes a signal transmitter which transmits a signal from the key input unit to the keyboard when the key input unit is removed from the holding section of the keyboard. The signal transmitter is made up of a light-emitting section and a light-receiving section. The light-emitting section is provided for the key input unit, and converts a signal entered from the key input unit into an optical signal and emits this optical signal. The light-receiving section is provided for the keyboard, and receives the optical signal emitted from the light-emitting section and converts the optical signal into an electric signal.