A computer system comprising: at least one display unit (151, 153); a first memory storing a first operating system and a BIOS; a subscriber identification module comprising: a second memory configured to store subscriber identification information and a second operating system different from the first operating system; and a second controller configured to perform an operation for the second operating system; a first modem connected via a prescribed interface to be driven by the first operating system; and a second modem connected via a prescribed interface to be driven by the second operating system, wherein the second modem is a mobile communication modem; and a first controller configured to load and use the BIOS to determine whether the subscriber identification module is connected via the prescribed interface and that the second operation system is installed in the SIM, and in response to the determining to control a booting of the first operating system via an operation of the first controller or a booting of the second operating system via an operation of the second controller or a booting of the first operating system and the second operating system to be selectively displayed on the at least one display unit (151, 153), wherein the first controller is further configured to perform, when the first controller determines that subscriber identification module is connected via the prescribed interface and the second operating system is not installed in the subscriber identification module, the booting of the first operating system and to control the second modem using the subscriber identification information to perform a data communication via a mobile communication network by executing an application emulating the second operation system in the first operating system; and wherein the first controller is further configured to perform, when the first controller determines that the subscriber identification module is not connected, the booting of the first operating system. at least one display unit (151, 153); a first memory storing a first operating system and a BIOS; a subscriber identification module comprising: a second memory configured to store subscriber identification information and a second operating system different from the first operating system; and a second controller configured to perform an operation for the second operating system; a second memory configured to store subscriber identification information and a second operating system different from the first operating system; and a second controller configured to perform an operation for the second operating system; a first modem connected via a prescribed interface to be driven by the first operating system; and a second modem connected via a prescribed interface to be driven by the second operating system, wherein the second modem is a mobile communication modem; and a first controller configured to load and use the BIOS to determine whether the subscriber identification module is connected via the prescribed interface and that the second operation system is installed in the SIM, and in response to the determining to control a booting of the first operating system via an operation of the first controller or a booting of the second operating system via an operation of the second controller or a booting of the first operating system and the second operating system to be selectively displayed on the at least one display unit (151, 153), wherein the first controller is further configured to perform, when the first controller determines that subscriber identification module is connected via the prescribed interface and the second operating system is not installed in the subscriber identification module, the booting of the first operating system and to control the second modem using the subscriber identification information to perform a data communication via a mobile communication network by executing an application emulating the second operation system in the first operating system; and wherein the first controller is further configured to perform, when the first controller determines that the subscriber identification module is not connected, the booting of the first operating system.