View and/or Forget and Uninstall Unused COM Ports in Windows 7.

Windows by default generates a new COM port (including USB) number for every *new* device that connects to it. But occasionally, depending on software functionality or another reason, one may wish to “start over” at a lower number. This is done in the Device Manager through a simple selection of “Show Hidden Devices.” Well, you’d think, anyway. Likely you’ve already tried this and realized it does not work. Why these extra steps are required I don’t know, but they’re the very reason I’ve mostly switched to OS X and Linux. But here you go:

Click “START”, and in the “Search Programs and Files” box, type

Command

You should see “Command Prompt.” show up above. *Right click” and click “Run as Administrator.”

Image

At this command prompt, type

set devmgr_show_show_nonpresent_devices=1

Presse ENTER and then type the following followed by ENTER again:

start devmgmt.msc

Now, click “View” and then “Show hidden devices.”

win7_2

 

Now, all devices that Windows has “saved” a COM port for but is not actually connected will now show. Simply right click and “Uninstall” to release that COM port number for a new instrument. Don’t worry: this will not delete drivers or anything; the instrument that was previously associated with that number will simply be assigned an unassigned number upon connection.

source: http://support.microsoft.com/kb/315539

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