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Some piece of software or some driver appears to be using the serial ports COM3-COM49.

New COM ports for Bluetooth et al get assigned ridiculous numbers over 50. When I try to change the number, Windows claim that the lower COM port number is in use, and suggest that I don't apply new settings. However, ActiveSync docs say that COM port number must be 20 or lower.

I have no idea where to look to figure out what's reserving the all those COM port numbers. What other ways do I have for uninstalling devices that don't appear in device manager? How do I figure out what took over those COM port IDs?

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up vote 7 down vote accepted

Go to My Computer, Properties, Advanced, Environment Variables, and make a System variable named


Make its value 1.

Now go to device manager, view, and check Show Hidden Devices.

Now expand Ports(COM & LPT). You'll see more ports than you did before. Right-click on and Uninstall whichever of the greyed-out ports you don't want.

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Thank you very much! Removing them will take a while though :-) – Ivan Vučica Nov 4 '09 at 21:09
Thanks! Here's the MSDN link (also works for Windows 7) – tamberg Jun 2 '10 at 15:41

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