I have phantom serial ports in Windows XP. How can I remove them?

The first step of removing the phantom ports is to remove all non-standard COM ports (remove any Multi-port serial adapters from the device manager).

Most likely there are leftover entries in the registry. You can run regedit to remove the extra entries.

  • NOTE: make a backup of the registry prior to taking any of the following steps. You edit the registry at your own risk.

    Run regedit. Go to: HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control/COM Name Arbiter

    Your system probably has:

  • The Data field of COMDB = FF FF FF 03 (or something similar).

    It should have:

  • COMDB = 03 00 00 00, if you have 2 built-in serial ports (or 01 00 00 00 if you only have one built-in COM port).
  • NOTE: 03 in binary is 0000 0011 so the lowest bit set (the 1 on the right) means COM1 is in use, and the bit to its left, in the 2 position, means COM2 is set.

    You will also want to clean keys for any non-standard serial ports from these places:

  • HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Windows NT/CurrentVersion/Ports

    You should be able to power down and reinstall the Digi adapter if it had been removed from the system. If it is installed, reboot the system. The adapter should be redetected and the driver installed. The com ports should now default to start at COM3 (or COM2 with only one built-in serial).

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