How to Delete COM Port In Use?

Every time you plug in a COM or USB device to your computer, Windows creates a virtual COM port and assigns it for a device. Every COM port has its number from 1 to 255. Also, each port is assigned exclusively for one device and remains occupied (Windows shows it as “in use”) even if the device itself is not plugged in anymore. Most of the time this is not a big deal or problem unless a user tries to run some ancient software that has trouble working with COM-ports higher than 9. For example, a piece of software may work well with COM1 to 9 but fail if there are no free COM ports below COM10. Another issue may appear when some specific devices take too many ports. For example, some adapters may reserve up to 30 or even more COM ports. In such scenario you are forced to delete COM ports in use in Windows or reassign a used COM port to a different device. In this article, we will show you how to do this.

Clear COM Ports in Use

There are different methods of how to delete COM ports in use. Luckily, there are different apps with a decent UI you can use to work with COM ports on your computer. Windows stores COM ports assignments in the registry key called COM Name Arbiter. We will show how to use the Registry Editor to clear or reassign COM ports, but first let us focus on more user-friendly ways to delete COM ports in use.

Caution: Before deleting COM ports in use, make sure to create a system restore point. Having a backup gives you a path back in case something goes wrong. The system restore point will help you to go back quickly and restore your system functionality.

Reassign COM Ports Using the Device Manager

First, let us go through the simplest method. You can quickly reassign COM port using the built-in Device Manager. This will work only if you have a free COM port you need to reassign. For example, Windows assigned COM24, but you need COM9 or any other COM port.

  1. On your keyboard, press Win + R and enter the devmgmt.msc command. This is a universal command that works in any recent Windows version; com port in use
  2. Locate the Ports section and expand it;
  3. Find the device you need to reassign COM port and right-click it. Select Properties;reset com ports windows 10
  4. In a new window, go to the Port Settings tab and press the Advanced button; delete com ports windows 10
  5. Select a new COM port number from the COM Port Number drop-down list at the bottom of a new window.com port in use windows 10
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This will work only if the COM port you need to use is free. If Windows says the port you need is in use, these instructions won’t work. Do not worry, though. You can manually delete the used COM port and reassign it for a new device.

Delete COM Ports in Use on Windows

  1. Open your system’s properties and press the Advanced system settings link; windows 10 com port in use
  2. In a new window, press the Environment Variables button; clear unused com ports windows 10
  3. In the User variables section, click the New button; com port in use by another application windows 10
  4. Set Variable name to devmgr_show_nonpresent_devices and the Variable value to 1;
  5. Now, launch the Device Manager using Win + R and devmgmt.msc command;
  6. Now you need to force the Device Manager to show disconnected and unavailable devices. You need this to delete COM ports in use. Press View – Show Hidden Devices;clear com ports windows 10
  7. The next step is to display all COM ports in use. Locate the Ports (COM & LPT) section. Do notice that every device shows which port it occupies. Tip: disconnected devices have translucent icons and devices you have plugged in to show a regular icon. Do not uninstall the devices currently connected;
  8. Find the port you need to free and right-click it. Select Uninstall. If some specific device occupies several ports simultaneously, you need to remove them altogether; how to reset com ports windows 10
  9. After this, Windows will free a port, so you can assign it to the device you need. Go back to the Reassign COM ports using the Device Manager section and follow it to reassign the port you just made free.

There is another way how to check which COM ports are currently in use. Although there is nothing wrong with using the Device Manager, you can check the list using it. Launch the PowerShell in Admin mode and paste the following command:

Get-WMIObject Win32_SerialPort | Select-Object Name,DeviceID,Description

clear com ports

Clear COM Ports Using COM Name Arbiter Tool

Also, you can easily delete COM ports with the help of a third-party tool called COM Name Arbiter Setter. It is completely free, and you can download it on the official website. This utility helps you to modify registry parameter ComDB simply without taking the risk to accidentally remove or edit wrong strings in the Registry Editor.

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Download the COM Name Arbiter Tool from the official website and run the executable file with Administrator privileges.

This tool’s main window shows the list of all COM ports and places a checkmark next to the currently occupied ports with present devices. If a device is not connected, hit Remove non-present devices. This will clear all assigned COM ports and make them available to assign. You can also clear the COM port manually, by unchecking a specific device from the list. This app automatically applies all the changes, so there’s no need to manually hit the Apply button.

how to clear com ports

Tip. You can also use a third-party tool called Device Cleanup Tool to remove non-present devices and clean up occupied COM ports. The Device Cleanup Tool is available for free from the official website.

Using DevCon to Delete Unused COM Ports

Also, you can clean up assigned COM ports with the help of DevCon utility that comes built-in with the Windows Driver Kit (WDK), Visual Studio, and Windows SDK for desktop apps.

  1. Run the Command Prompt as Administrator and paste the following command:
    Cd %WindowsSdkDir%\toolsx64
  2. List the reserved COM ports using the command:
    devcon findall =ports windows 10 com ports in use
  3. Now you can remove all unused ports using their IDs. For example:
    devcon remove @”PCI\VEN_8086&DEV_A13D&SUBSYS_30BE17AA&REV_31\3&11583659&0&B3” com port in use but not in device manager

Thus, you can delete all unnecessary COM ports (if you try to remove the used device, the Remove failed error appears) and reassign them to different devices.

Reset COM ports using the Registry Editor

Now, let us talk about the most challenging methods of how to delete COM ports in use. In this part, we won’t use any third-party tools. All is needed is the Registry Editor which is a part of every Windows installation.

Caution: Backup the important data and create a system restore point. Follow the instruction strictly and be careful not to edit random fields. Breaking the COM ports assignment registry key may end up getting lots of BSODs. We are pretty sure you don’t want this.

  1. Disconnect all peripheral devices;
  2. Press Win + R on your keyboard. Enter the regedit command to run the Registry Editor;reinitialiser port com windows 10
  3. Go to the following path: Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\COM Name Arbiter. If you use Windows 10, just copy the path, and enter it into the address field;
  4. On the left side of a window, right-click COM Name Arbiter and select Export. Save the export somewhere you can easily access it in case something goes wrong. In case of emergency, this will help you restore the previous working settings; release com port windows 10
  5. If you want to reset all COM ports, change the ComDB value to . ComDB’s binary value defines the list of reserved COM ports. Every bit defines the status of the corresponding port (1 to 255); delete com ports
  6. You can also find the list of all assigned COM ports in the Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Ports path. You can delete all the ports you want to free; reset com port numbers windows 10
  7. Restart your computer. When it boots back, connect all the devices in the proper order.
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That’s it! Now you know how to delete COM ports and reassign them to a different device.

29 comments

  1. I have tried this in Win 7 x64 and I do not see the ports that are not connected. I am using a USB to Serial adapter (FTDI – virtual com) and when the usb side of the device is connected to the computer it shows in Device Manager, when the usb side of the device is not connected to the computer is does not show in Device Manager (even when using your directions)

    Please advise!

    1. Windows 10:
      Right click start menu, click device manager.
      In top menu, click “show hidden devices”.
      Under COM ports, delete any ports you don’t want (right click and click delete).

      Exactly the same for Windows 7 except open device manager by right clicking on Computer either on your desktop (if it’s there) or in the start menu, select Properties and then click on Device Manager on the left side.

      I don’t why they give you all these arcane command line commands when it’s so simple to do the same thing in the GUI. After all, this is why GUIs were invented.

  2. I tested this just a few minutes ago and yes, it looks like it has changed a little bit. Got it working. You need to do this. Open up Command Prompt, type: set DEVMGR_SHOW_NONPRESENT_DEVICES=1 and then hit enter. Then type: start devmgmt.msc. Then go up to view and show hidden devices. It should now show up even when it isn’t plugged in.

  3. It worked! Non present devices show up with the port number assigned right next to it.
    That’s exactly what I needed.
    Thank you Brian for sharing your wisdom!

  4. First it didn’t worked for me. But then I booted in safe mode, and do this procedure.
    It still didn’t worked, but then I started deleting all unnecesarry devices like usb disk drives and stuff.
    After some while in Com&ports sections I managed to see some more devices with com ports assigned to them, and only then I could delete them.

  5. Worked like a charm, thanks! I suspected those little bastards were hiding somewhere and now I know how to find them. :o)

    To those not getting it to work, you are probably not managing to set the environment variable properly (step 2). No reboot is required and you can see that you were successful if you instead do it like this:
    * Bring up system properties dialog (Win+Pause alt. System in Control Panel) (In Vista/7 also click “Advanced system settings”)
    * Go to the advanced tab and click the “Environment variable…” button. (Hint: You can also find the device manager in the hardware tab in the same dialog, unless you want to show off your command line ninja skills of course. ;o))
    * Click a “New…” button, preferably the upper one but it doesn’t really matter.
    * Fill in variable name devmgr_show_nonpresent_devices and Variable value 1.

    After this all you have to do is reopen the dialog. (Tried on Win XP and Win7)

  6. Thanks, worked a treat in Windows 7 (no reboot was required) when I replaced my motherboard. The com ports werent working and on checking the ports in use there were twice as many as there should be. Your tip allowed me to get rid of the old ones.

  7. For windows 7 32bit, etc, be sure you are in the Windows directory. Type: cdWindows once you are int he command prompt, then follow steps 2,4,5,6 above.

  8. Works, but I can only uninstall some comports, but not all are show, so I can’t free all my comports.

    It does show nicely all my connected and unconnected devices.

  9. Hi Brian, got a quick question…what if you uninstall all the COMs and reboot but the COM ports come back and still show that they are in use when there is nothing being shown for the device(s)?

  10. Ok I figured it out never mind printers, removing to get comports etc..
    Com Ports will not show until you connect a comport. So even though your comport is high and unusable (for a test) go ahead and activate it only then will you see it listed under ports you’ll see the comport shows up but its likely too high for your application, just an exercise so you can see comports will only show if you have something paired.
    Now the reason you have all these unused comports is because drum roll …you have plugged in a multiple USB hub get it ? The hub causes unused com ports to be assigned so when you pair the one com port you need its sequentially high on the list, a number that won’t work. Remove the external hub then create the com port (pair) the one you want, once paired you’ll find your assigned a lower usable comport. Then, if you want, plug the hub in and it will assign comports above the lower number one you just installed. Computer will remember the comports unless you remove the lower comport, no worries just repeat the process to get the right comport.
    Hope this works for you!

    1. 1. Write down the name of the port used for the connection.
      2. Open the printer screen so that the printer’s port settings can be changed.
      3. Right-click the printer icon, and then;
      Windows 7 / Window 8 /Windows 10:
      click [Printer Properties].
      Windows XP / Windows Vista:
      click [Properties].
      5. Click the [Ports] tab.
      6. Select the port name confirmed in step 2 (“COM” plus a number).
      7. Click [OK] to close the properties dialog box.

      or you can try to create Virtual Serial Port with the help of virtual-serial-port*org and assign a COM port for the printer.

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