Original: Because there are two separate controllers in each USB 3.0 host , USB 3.0 devices will transmit and receive at USB 3.0 data rates regardless of USB 2.0 or earlier devices connected to that host .
Simplified: On an USB 2.0 controller , standards can be mixed . Devices connected to a USB 1.1 hub will only go as fast as USB 1.1 rates .