A computer system includes a system part, a connector to which an external device is connected, a communication unit which performs communication with the external device, and a control unit which is connected between the connector and the communication unit to monitor a state of a predetermined recognition signal applied from the external device when the system part is in a standby mode. The control unit performs a predetermined function corresponding to the monitored state of the recognition signal. When the system part is in the standby mode, the system part may be switched to an operation mode based on the recognition signal from the external device. Additionally, a predetermined charging power is output to an external device in response to the predetermined recognition signal applied from the external device connected to the connector while the system part exists in the standby mode.