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At work, I want to plug all my USB devices into a single USB hub so I only need to plug one USB cable, external display, and the power cable into my laptop. I have some USB 3.0 devices and some slower USB 2.0/1.1 devices.

I'm aware that all the devices on a single USB Root Hub share the same bandwidth, but I'm curious whether plugging an older device into a hub causes the entire hub to fall back to a compatibility mode.

If I plug the slower devices into my USB 3.0 hub, will that hub and all its connected devices slow down to USB 2.0 speeds, or will the USB 3.0 devices continue to run at USB 3.0 speeds?

For example, suppose I have an USB 3.0 gigabit network adapter and an USB 2.0 keyboard. If I plug the keyboard into the same USB 3.0 hub that the network adapter is plugged into, will the network adapter's maximum theoretical throughput instantly drop to 480 Mbps or slower (USB 2.0's maximum throughput)?

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2 Answers 2

up vote 13 down vote accepted

Short answer: No.

Long answer:

I stumbled across part of the answer to my question in a comment to an answer for a seemingly unrelated question. It turns out USB 2.0 and USB 3.0 are physically segregated in the wiring. But as Ben Voigt points out, the segregation is also done at the port level within each bus: ...each downstream port negotiates its own speed, then data is buffered and forwarded upstream at the maximum speed of the upstream link.

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Nice find! Guess you can accept your own answer. :) –  Karan Sep 20 '12 at 0:25
This long answer is wrong. It's actually the ports that are segregated. If it were done as described in your answer, then a single USB 2 low-speed device would cause all USB 2 full-speed and high-speed devices to operate at low-speed, and only USB3 devices would be faster. But actually each downstream port negotiates its own speed, then data is buffered and forwarded upstream at the maximum speed of the upstream link. –  Ben Voigt Jul 17 at 17:01
@BenVoigt I had only considered the physical connectors and wires originally. Thanks for the clarification. –  rob Jul 18 at 18:09

I wanna tell you how to imagine speed in wires.
It is like a tunnel (water transfer tunnel).
Assume a big tunnel is splitted into several same size tunnels (HUB) and you connect your 2.0 device (which is a smaller tunnel comparing to 3.0) to the hub.
What will happen? Does the other tunnels get smaller? NO! Your 2.0 device uses as much speed as he can.
This imagination really helped me to understand network problems. (Thanks to TV Programs!)

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This answer isbt really helpful. It also contains numerous grammar mistakes –  Ramhound Sep 22 at 20:57
What r u looking at? Edit it! –  UltraDEVV Sep 22 at 21:00
Why don't you edit, improve it, and post a quality answer. I don't like to edit grammar mistakes on my own unless it's in the review queue –  Ramhound Sep 22 at 21:03
Is it good now? I am Intermediate in English. So it is wise to get your vote down back. OK? –  UltraDEVV Sep 22 at 21:06
I didn't issue the downvote –  Ramhound Sep 22 at 21:07

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