You may have heard that USB 2.0 is "backward-compatible" with USB 1.0/1.1 (Full-Speed USB). While that's true, USB 1.1 is also forward-compatible with USB 2.0. Whenever a system has USB 2.0 ports, you'll find the "Enhanced" USB controller in Device Manager, but you will also find two other USB controllers. These two to mantain backward compatibility to USB 1.1 devices. Each USB 2.0 host actually has 3 chips onboard. The USB controller routes signals to the correct controller chip depending on how a device is recognized. Where a device is physically plugged in has no bearing on how it is routed. All ports on a USB 2.0 motherboard can host any USB devices at all as long as the system and devices are healthy.
The vast majority of USB 2.0 devices will work on older PCs and Macs. None should flat-out fail unless there are other issues with the system. Hi-Speed USB devices will revert to Full-Speed operation when connected this way. Understand that Hi-Speed is at least ten times faster than Full-Speed in actual operation, so the speed difference is quite noticeable? unless you have never experienced Hi-Speed, of course.