Tech Blog


Get extra COM ports to appear in Device Manager

Posted in Windows by Ed Ross on August 12, 2007

Another tip from guest James Saunders:

I noticed while configuring my Bluetooth devices that they were using quite high COM port numbers (COM8, COM9, COM10), and each time I installed a new device the COM port numbers would keep on rising.
Windows has a habit of assigning COM ports to connections which, even after the device is removed, still remain allocated to that device. As you connect new devices they get assigned the next free COM port number, and before you know it, you are using COM ports 30-40.
Although they are configured in Windows, they will not show up when viewing the hardware configuration in control panel. These COM ports can not be seen even after selecting ‘Show Hidden Devices’. The only time these COM Ports are visible is when the device is connected.

In order to get these extra COM ports to appear in Device Manager, perform the following steps:

  1. Click Start -> Click Run
  2. Type ‘cmd.exe’ in the textbox and click OK.
  3. Type ‘set devmgr_show_nonpresent_devices=1’ and hit ENTER.
  4. Type ‘cd \windows\system32’ and hit ENTER.
  5. Type ‘start devmgmt.msc’ and hit ENTER.
  6. When the Device Manager opens, click View -> Show Hidden Devices.
  7. Click on the + sign next to the Ports to see the full list of COM ports being used.
  8. Highlight the port you wish to delete and then press delete. Accept when asked to do so and continue with any more that you wish to delete.

Thanks James!

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2 Responses to 'Get extra COM ports to appear in Device Manager'

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  1. I found this particular tip of greatest use when using a Bluetooth USB dongle, they sometimes use up a new COM port up each time they are plugged in.

  2. jonnyh said,

    hmm thats interesting. I had this issue at work where an IBM thinkpad which had onboard bluetooth did some odd things wanting to use umpteen com ports, I put on the newest bluetooth drivers on then went into the bios and set it to load defaults, thinking there was a hardware IRQ setting somewhere.

    This turned out to be a huge mistake as the laptop would then bluscreen when booting, and not even last good known configuration or safe mode would make it boot properly. I had to get into work early the next day and do a repair install of XP to make it functional again (I disable bluetooth this time) as the engineer needed the laptop to do his exam later that morning. I let the other IT helpdesk worry about bluetooth for another time, as the machine had some stability issues and needed a full reimage.


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