A distinguishing circuit includes first to fifth resistors, a front panel connector, and a jumper. The front panel connector includes first to tenth pins. When the ninth pin is connected to the tenth pin through the jumper, a BIOS (Basic Input Output System) chip will determine whether a computer system is a first type. When the eighth pin is connected to the tenth pin through the jumper, the BIOS chip will determine whether the computer system is a second type.