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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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For connecting USB 1.1 devices to USB 2.0 hub, it depends on whether the hub has a single or multiple transaction translators. For USB 2.0 devices in USB 3.0 hub, there is apparently no such thing, though: en.wikipedia.org/wiki/USB_hub#Transaction_translator – endolith Feb 4 at 15:11
up vote 22 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
    
@BenVoigt I had only considered the physical connectors and wires originally. Thanks for the clarification. – rob Jul 18 '14 at 18:09
    
@Ben Can you clarify something? If I have two USB2 webcams, normally each would saturate a USB2 link. If I connect both to a USB3 hub, are you saying that they would each be able to use 480 Mbps since the hub would aggregate traffic and resend over the 5 Gbps USB3 link to host? – Nicu Stiurca Sep 30 '15 at 14:16
    
@SchighSchagh: Yes, barring some major design problem in the hub, that's exactly the advantage. (Well, neither device will reach 480 Mbps, but they will each receive as much bandwidth as if there were no other device attached) – Ben Voigt Sep 30 '15 at 14:37
    
@SchighSchagh Wikipedia says that doesn't happen: en.wikipedia.org/wiki/USB_hub#Transaction_translator – endolith Feb 4 at 15:28

No.

Here is how to imagine speed in wires.

Think of it like a tunnel that transfers water.

Assume a big tunnel is split evenly into several similarly-sized tunnels (HUB). Next, you connect your 2.0 device (which is a smaller tunnel comparing to 3.0) to the hub.

What happens? Do the other tunnels get smaller? No, they do not. Your 2.0 device uses as much speed as it can.

This analogy really helped me to understand network problems.

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This analogy is not correct for a wide variety of network (really "bus") situations. For example, USB 1 devices on USB 2 will slow the bus down by occupying a disproportionate amount of time for the data transferred (blocking other, faster devices from using the bus). Same for 10mBit devices on Gigabit networks. RS-485, SATA, and other serial buses only go as fast as the slowest device. Not true for USB3 however, because the cable contains DIFFERENT WIRES for v.2 and v.3 of the protocol. It's the difference between putting minivans and Ferrari's in the same lane vs each getting their own lane. – DrFriedParts Jun 22 at 11:11

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