Processing apparatus and operating system

Disclosed is a processing apparatus which is coupled to a host apparatus through a connecting device. The processing apparatus comprises a connection port, a control unit and a switching unit. The connection port is used for connecting the connecting device. When the connecting device is coupled between the connection port and the host apparatus, the control unit controls all switching signals based on the varieties of the connecting device. The switching unit determines whether an external voltage should be supplied to the control unit or not based on the switching signal. When the switching unit provides the external voltage, the control unit operates based on the external voltage. When the switching unit does not provide the external voltage, the control unit operates based on a host voltage provided by the host apparatus. The external voltage is provided by an external apparatus.