# What app is using the Com Port? **URL:** \ **Category:** Factual Questions\ **Created:** [January 8, 2010, 4:04pm UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167 "2010-01-08T16:04:19Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [January 8, 2010, 4:04pm UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/1 "2010-01-08T16:04:19Z")
Windows XP, service pack 2. An app trying to connect to a device on the com port reports that another app is using it. How can I determine what the other app is? Thanks! ---
**Author:** ![krebbin](https://avatars.discourse-cdn.com/v4/letter/k/85e7bf/32.png) [@krebbin](https://boards.straightdope.com/u/krebbin)\ **Post date:** [January 8, 2010, 9:35pm UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/2 "2010-01-08T21:35:23Z")
These days modems are usually the only things that use com ports. You can check whether one is being used under Control Panel, Phone and Modem, then pick the Modem tab. It will tell you if there’s a Com port assigned to it. Hope this helps:-) ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [January 8, 2010, 10:10pm UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/3 "2010-01-08T22:10:47Z")
Thanks, but there is no modem. I suspect it is a virtual comm port. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [January 8, 2010, 10:15pm UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/4 "2010-01-08T22:15:19Z")
DO you have UPS (battery backup) power supply software installed? ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [January 8, 2010, 10:16pm UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/5 "2010-01-08T22:16:19Z")
Also; sometimes using COM1 will tie up COM3, COM2 ties up COM4, depending on software. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [January 8, 2010, 11:00pm UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/6 "2010-01-08T23:00:54Z")
If I recall correctly, Process Explorer (which you can download from Microsoft) will tell you what files, dlls, devices, etc. all of your process are using. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [January 9, 2010, 5:04am UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/7 "2010-01-09T05:04:59Z")
Other than modems bluetooth drivers will virtualize com ports and older PDA IO software can tie up com ports. If the system is an older notebook that has infrared IO that can also use com ports. ---
**Author:** ![sharding](https://avatars.discourse-cdn.com/v4/letter/s/90db22/32.png) [@sharding](https://boards.straightdope.com/u/sharding)\ **Post date:** [January 9, 2010, 7:05am UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/8 "2010-01-09T07:05:02Z")
I have nothing useful to add, but I just have to share that when I read the thread title, I originally thought it said “Corn Port.” And yes, I know what a com port is, so I don’t know why my brain processed it that way. I’m not sure I want to know what a corn port is… ---
**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\ **Post date:** [January 9, 2010, 7:09am UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/9 "2010-01-09T07:09:07Z")
Read Faulkner. _Sanctuary_. ---
**Author:** ![krebbin](https://avatars.discourse-cdn.com/v4/letter/k/85e7bf/32.png) [@krebbin](https://boards.straightdope.com/u/krebbin)\ **Post date:** [January 9, 2010, 10:41am UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/10 "2010-01-09T10:41:34Z")
> [@carnivorousplant](#): > > Thanks, but there is no modem. I suspect it is a virtual comm port. Well I’ve just checked my Modem Options. I have one listed which is my Bluetooth device, on Port 14. I’m surprised it didn’t pick port 1,2 or 3. So as you suggest it must have created a virtual port:) The question then, is why doesn’t your app do the same?😕 As already suggested by Mr Geek, Process Explorer may help you ascertain what is hogging your systems resources. ---
**Author:** ![Khadaji](https://avatars.discourse-cdn.com/v4/letter/k/9e8a1a/32.png) [@Khadaji](https://boards.straightdope.com/u/Khadaji)\ **Post date:** [January 9, 2010, 12:07pm UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/11 "2010-01-09T12:07:03Z")
Do you have a firewall? I have a USB to Serial adapter for some software I am developing and my firewall would not allow me to open the port. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [January 11, 2010, 10:06pm UTC](https://boards.straightdope.com/t/what-app-is-using-the-com-port/524167/12 "2010-01-11T22:06:11Z")
> [@engineer\_comp\_geek](#): > > If I recall correctly, Process Explorer (which you can download from Microsoft) will tell you what files, dlls, devices, etc. all of your process are using. I didn’t find it by device, but a Company Name that I did not recognized proved to be it. thanks!