In order to be backward compatible with the old motherboard, the current operating system will keep the original motherboard with two COM ports. When adding USB port or other ports, that is, adding COM port, the system will start from COM3 by default instead of COM 1.

To modify the serial number of COM port: enter Device Manager-Ports-Selected Point Properties-Port Settings-Advanced -COM Port Number Settings. As long as it does not conflict with existing ports.