[SOLVED] Total Bandwidth for Multiple USB 2.0 Devices in a USB 3.0 hub

[tommy59375]

Suppose I have a fully compliant 4 port USB 3.0 hub plugged into a USB 3.0 port on my computer. The system is therefore capable of a bandwidth of 5 Gbps.

My question is this: If I fill all 4 ports with USB 2.0 devices, are they all able to operate at the full USB 2.0 speed at the same time (4 lots of 480 Mbps each i.e. 1.92 Gbps in total) or does the hub need to serve those devices in some sort of "legacy mode" which limits the total throughput to 480 Mbps instead? Thanks.

----------

EDIT. For anyone stumbling across this page from a search engine in the future, this Superuser thread has the answer:
https://superuser.com/questions/590668/understanding-power-and-data-bandwidth-when-using-usb-2-0-devices-on-a-usb-3-0-c

The four USB 2.0 devices will need to share a total of 480 Mbps between them, even if connected to a USB 3.0 hub. They will not be able to operate concurrently at full speed. Instead, they will only have one-quarter of the maximum USB 2.0 bandwidth available to them. This is because, effectively, a "USB 3 hub" is actually two dedicated hubs in one box -- one for USB 2.0 data and another for USB 3.0 data.

Here is a diagram of the hypothetical situation. Despite all being connected to a USB 3.0 hub (which is connected via a USB 3.0 cable to a compatible PC), the four hard drives must share the bandwidth of a single USB 2.0 link.

 

[jojesa]

You never going to achieve the USB 3.0 5 gbps (640 MBps) theoretical (on paper) data-transfer speeds. The same applies to USB 2.0
The maximum USB 3.0 I have seen does not even go above 200 MBps.
If you connect several USB devices to the same USB hub bandwidth will be divided into all connected devices.

If you connect USB 2.0 to USB 3.0 hub, USB 3.0 will default to USB 2.0 speeds.

 

[tommy59375]

You never going to achieve the USB 3.0 5 gbps (640 MBps) theoretical (on paper) data-transfer speeds. The same applies to USB 2.0
The maximum USB 3.0 I have seen does not even go above 200 MBps.
If you connect several USB devices to the same USB hub bandwidth will be divided into all connected devices.

If you connect USB 2.0 to USB 3.0 hub, USB 3.0 will default to USB 2.0 speeds.

This does not answer the question.

To rephrase:

- If I plug four USB 2.0 devices into a four port USB 2.0 hub, they won't all be able to operate at their full speed concurrently, because the hub is only connected to the computer with a single USB 2.0 link. That is, the connection from the hub to the computer is a bottleneck if two or more of the devices require more bandwidth (in total) than a single USB 2.0 link can provide.

- USB 3.0 has approximately ten times the bandwidth of USB 2.0.

- So, if I plug four USB 2.0 devices into a four port USB 3.0 hub, will all four devices be able to operate at their full speed concurrently, thereby avoiding the bottleneck described above? Or will the hub not be able to take advantage of the faster connection it has to the computer, because the four devices connected to the hub are each only USB 2.0?

 

[jojesa]

Even though you down voted my post I will give you the answer using different explanation.
When I said hub above, I was referring to the internal USB hub on your system.

If you connect any USB 2.0 device into a USB 3.0 USB port, the USB 3.0 will work as a USB 2.0.
So there will be no advantages whatsoever on connecting USB 2.0 into USB 3.0.
You could down vote the post again but that won't make your USB 2.0 work faster because you are plugging it into a USB 3.0.

 

[tommy59375]

Even though you down voted my post I will give you the answer using different explanation.
When I said hub above, I was referring to the internal USB hub on your system.

If you connect any USB 2.0 device into a USB 3.0 USB port, the USB 3.0 will work as a USB 2.0.
So there will be no advantages whatsoever on connecting USB 2.0 into USB 3.0.
You could down vote the post again but that won't make your USB 2.0 work faster because you are plugging it into a USB 3.0.

Isn't that what the up/down vote system is for? Maybe it's a little harsh, but in my book a post which doesn't answer the question should get a down vote.

I'm not asking if a USB 2.0 device can "work faster" by being plugged into a USB 3.0 port, and neither am I asking about theoretical versus real world performance. Perhaps this is a language issue. Regardless, it doesn't matter because I've found the answer online now. Thanks for your time anyway.

----------

For anyone stumbling across this page from a search engine in the future, this Superuser thread has the answer:
https://superuser.com/questions/590668/understanding-power-and-data-bandwidth-when-using-usb-2-0-devices-on-a-usb-3-0-c

The four USB 2.0 devices will need to share a total of 480 Mbps between them, even if connected to a USB 3.0 hub. They will not be able to operate concurrently at full speed. Instead, they will only have one-quarter of the maximum USB 2.0 bandwidth available to them. This is because, effectively, a "USB 3 hub" is actually two dedicated hubs in one box -- one for USB 2.0 data and another for USB 3.0 data.

Here is a diagram of the hypothetical situation. Despite all being connected to a USB 3.0 hub (which is connected via a USB 3.0 cable to a compatible PC), the four hard drives must share the bandwidth of a single USB 2.0 link.

 

[Ralston18]

I "undid" the -1.

Sure downvotes have a purpose but should not be so quick and so "harsh".

Certainly a legitimate question and discussion. And either one (question or response) may need some clarification and refinement.

That is part of the process...

First ensure that everyone is in agreement with the topic and circumstances.

And maybe wait for some additional input and comments - there may be other factors and considerations.

 

[jojesa]

Thanks, Ralston18
It won't be my first or last.
By reading the lengthy explanation on that website, I think it could be summarized into this sentence from my first post

If you connect several USB devices to the same USB hub bandwidth will be divided into all connected devices.

 

[tommy59375]

Thanks, Ralston18
It won't be my first or last.
By reading the lengthy explanation on that website, I think it could be summarized into this sentence from my first post

If you connect several USB devices to the same USB hub bandwidth will be divided into all connected devices.

Sorry Jojesa, it's my fault for not elaborating. Clearly I didn't manage to do a good enough job of getting the nuance of my question across properly and I should never have downvoted your post as you didn't say anything inaccurate or incorrect. I apologise for wasting your time.

But now look what I've gone and done...
I clicked the 'down' arrow to try and reverse the downvote and somehow I managed to click it on your second post instead of the one I downvoted in the first place. Only now do I realise that I can't undo that! Oh dear. I think I'd better leave this thread alone before I manage to do any more damage!