If you use USB dongles for serial adapters, then each path through USB is assigned a different COM number when you plug it in. For example if you plug into USB

If you use USB dongles for serial adapters, then each path through USB is assigned a different COM number when you plug it in. For example if you plug into USB controller 2, port 3 which goes to a hub, and then you plug into port 2 that gets a number. Now plug the same thing into a different port and it will get another COM number. Under the hood this is because the USB devices do not have the (optional) unique serial number (or in some cases they all get the same serial number). https://devblogs.microsoft.com/oldnewthing/20041110-00/?p=37343 https://devblogs.microsoft.com/oldnewthing/20041110-00/?p=37...