My computer (running Windows XP) has 4 USB ports at the back. From the Device Manager window, I know that one of them is 2.0, and the rest are all 1.0. I have a webcam that I think will benefit from the increased speed if I plug it into the 2.0 port. But how do I tell which one?
If you have a USB2 controller in your device manager then all the ports on your motherboard should theoretically be able to use full USB2 speeds.
USB 2.0 operates over the same infrastructure (ports) as USB 1.x but changes the operation of the system and only requires 1 root hub for all the ports instead of individually addressed ports for USB1.x. A USB 2.0 device plugged into a USB1.x port that has a USB2 controller as the root hub will be able to operate at USB 2 speeds for all the ports that are connected to it, which is typically all the ports that your motherboard supports.
If you plug a USB 1.x device into that same port then the controller will pass the data through to the USB 1.x controller seamlessly.
One way to test this would be to plug in a USB thumbdrive and copy one large file to it.
Repeat this for every USB port, and you will have noticed which one was significantly faster than the others. Solved!
(There might be an elegant trick inside Windows to figure this out, but I can't think of it at the moment.)