It's all about the Software

ok, now i understand.... clear explanation on this webpage!.
So it's not a USB3 bandwith or interupt issue

The point is that USB3 is not USB3 when talking to USB2 devices, the devices talk one at a time, and speed changes take some time to establish themselves at all. So saying USB3 has humongous bandwidth resource ONLY holds when ONLY USB3 devices are connected to it. USB2 devices use up available USB3 bandwidth to the same ratio as it eats up available USB2 controller bandwidth. That is critical to understand.

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