Abstract: A host computer formed of a motherboard, a power supply unit with a power switch, a data storage device and an external interface is disclosed to have a transfer switch switchable between a first switch position and a second switch position, the transfer switch having three contacts in the first switch position for electrically connecting the motherboard to the power supply unit and the data storage device to the power supply unit and the motherboard to the external interface, and two contacts in the second switch position for electrically connecting the data storage device to the external interface through a data transmission interface and the data storage device to said power supply unit respectively. This design allows access to the data storage device, achieving the effect of sharing the data storage device without booting the computer system.

Abstract: A selectable backup power supply device for providing power to a real time clock (RTC) and a memory unit is disclosed. The device includes a backup battery, a first power outputting unit and a second power outputting unit, wherein the backup battery outputs a backup voltage, the first power outputting unit is connected to the backup battery and the RTC for receiving the backup voltage and outputting a first supply voltage to the RTC, and the second power outputting unit is connected to the backup battery and the memory unit, for receiving the backup voltage and, in accordance with a selection signal, outputting a second supply voltage to the memory unit or stopping the output of the second supply voltage.