Is a USB Hub slower when multiple devices are connected ?

[Coulous]

Hello,

Well, I'm changing my desk setup, and it turns out that my PC will be under the desk. It will be a bit far, so I'm thinking of getting a USB hub to make my life easier. But one thing I don't actually know is if I take a hub, plug it into a USB port, what if I plug 2 USB devices at the same time on it then ? Will the speed be divided by 2 ? Might be a stupid question, but I'd really like to know.
Oh, and do you guys have one to recommend me ? 

 

Thank you !

[minibois]

The hub usually has a system inside that will give a device as much bandwidth as it needs, but if both need the max bandwidth, it will slow them down.

See it like this; a USB 3.0 hub has 5Gb/s input. If both devices (or more) connected to it also require that speed, it can of course never give both the max speed.

[akio123008]

Whether it's a problem is another matter; unless your devices are going to be doing something like copying files at the same time, the speed decrease probably doesn't matter.

[SupaKomputa]

Yes, the max bandwidth will be shared.

 

[Archer20]

It's something called "half duplex". If the devices are all trying to transmit at the same time, yes there will be "collisions" and slowdown.

[Kisai]

27 minutes ago, Coulous said:

Hello,

Well, I'm changing my desk setup, and it turns out that my PC will be under the desk. It will be a bit far, so I'm thinking of getting a USB hub to make my life easier. But one thing I don't actually know is if I take a hub, plug it into a USB port, what if I plug 2 USB devices at the same time on it then ? Will the speed be divided by 2 ? Might be a stupid question, but I'd really like to know.
Oh, and do you guys have one to recommend me ? 

 

Thank you !

The entire bandwidth with be consumed by the first device on the lowest numbered port on the hub, and when you plug in subsequent devices, they will be starved of bandwidth if they try to use more than the upstream port has available. This is typically why every high speed device says not to use a USB Hub.

 

You can use a Hub, you just can't use two high speed devices on one. So if you have a 4K camera and a SSD connected to a hub connected to the same port, both will suffer, but the camera will suffer more since it can't dial back it's bandwidth unlike the SSD. It won't know which device has more priority.

 

To be safe, only low bandwidth devices should be plugged into hubs (eg mouse, keyboard, graphics tablet, gamepads, etc) and even then, high-dpi devices might start malfunction since they require a higher bandwidth entirely for the interrupt rate.

[Archer20]

6 minutes ago, Kisai said:

The entire bandwidth with be consumed by the first device on the lowest numbered port on the hub, and when you plug in subsequent devices, they will be starved of bandwidth if they try to use more than the upstream port has available. This is typically why every high speed device says not to use a USB Hub.

 

You can use a Hub, you just can't use two high speed devices on one. So if you have a 4K camera and a SSD connected to a hub connected to the same port, both will suffer, but the camera will suffer more since it can't dial back it's bandwidth unlike the SSD. It won't know which device has more priority.

 

To be safe, only low bandwidth devices should be plugged into hubs (eg mouse, keyboard, graphics tablet, gamepads, etc) and even then, high-dpi devices might start malfunction since they require a higher bandwidth entirely for the interrupt rate.

Excellent explanation for him. Here I am using terms like half duplex and collision(referencing packet collision in a net hub). Sometimes I speak too much like an engineer

[Coulous]

Alright, thanks guys ! So it's not an ideal solution but it's ok if I do not use really fast devices simultaneously then. I guess it will do.
But is there another way ? Just in case !

[Kisai]

1 hour ago, Coulous said:

Alright, thanks guys ! So it's not an ideal solution but it's ok if I do not use really fast devices simultaneously then. I guess it will do.
But is there another way ? Just in case !

You can buy USB 3.0/3.1 gen 2 extension cables, but be aware that there is a maximum distance. 

 

Generally there is not much practical use for USB hubs at all unless you're plugging in a dozen USB 2.0 USB pen-drives that you aren't actively using all at once, or you have a bunch of USB audio equipment like MIDI controllers that aren't high bandwidth at all.