Configuration of COM Ports
Starting with Windows 2000, a COM port is a type of serial port that complies with the following additional requirements:
You access the COM port through an instance of the COM port device interface class. The GUID for this class is GUID_DEVINTERFACE_COMPORT, which is defined in Ntddser.h.
You operate the COM port by using the 16550 UART-compatible interface that is defined in Ntddser.h.
To ensure compatibility with most applications that access COM ports, you should assign a symbolic link name that uses the standard naming convention "COM<n>", where <n> is the COM port number (for example, COM1). If you use a COM<n> name, you must obtain the COM port number <n> from the COM port database. COM port numbers should only be used with COM<n> names.
By default, the combined operation of the class installer for the Ports device setup class and the Serial function driver configure a device as a COM port.
For information about how the Ports class installer and Serial create a COM port device interface for a COM port, see External Naming of COM Ports.