HKLM\SYSTEM\CurrentControlSet\Services\Serial\
This subkey is added to the registry, but it is not used by Windows 2000.
In Windows NT 4.0 and earlier, this subkey contained subkeys representing specific serial ports on the computer. In Windows 2000, settings for individual ports are stored in device-specific subkeys of Enum subkey (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum).