A convertible computer is equipped with a notebook computer function and a tablet computer function. When a system power supply is turned on, a functionality or physical configuration such as rotation state of a display module can be detected, and an environment can be controlled such as an operating system (OS) for a tablet computer or notebook computer is selectively booted. Input signals of input units can also be controlled in an activation or inactivation state according to a system mode. An operation of switch sensing an open/closed state of a liquid crystal display (LCD) can be controlled by a signal generated by the rotation operation of the display module. In a state in which at least one control value necessary for setting a system environment is stored in a memory, the system mode switching operation is monitored and the system environment is set according to the switched system mode.