USB hubs - some guiding principles please

  Diemmess 17:49 20 Dec 04
Locked

Will soon have a "spare" usb hub as part of a software deal.

How does the pecking order run? At the moment I have 6 USB sockets 2 (USB1) from the mobo and 4 (USB 2) from a PCI card. Everything works fine but what must I avoid to keep it that way?

"Don't fix it" does not qualify as an answer!

  Fruit Bat /\0/\ 18:01 20 Dec 04

IS hub USB1 or 2? Powered or not?

USB1 hub will drop speed of port if pluged into USB2 port.

Rember the hub draws its power from the port so if not seperately powered then power hungry devices (scanner/printer) may overload the port and programs can freeze.

  Diemmess 18:27 20 Dec 04

Until I see it. I have no idea.

Obviously will use it where there is no potential power demand, but how fixed is a particular USB socket to a dependant piece of hardware?

For instance, I have USB connections to a printer (self powered) a camera, a memory stick and a joystick, none of which (I suppose) have serious power demands. An external HD goes to a USB2 socket, though this too has its own power supply

On the other hand I have a BB modem at present on one of the USB 1 sockets.

I don't (yet) need the hub. It is sure to be a cheapo one, but nice to have as a standby. If I plug it in to a USB2 socket and the hub is only USB1 it will only slow down its dependant sockets, won't it?

  Diemmess 17:49 23 Dec 04

The device claims to support either USB1 or 2 (presumably depending on the status of the "host" socket)

Fundamentally then, there must be a top limit on the number of devices which can be plugged into one computer....... Assuming that we are not using appreciable power (for data only devices) then how many can one computer take?

Or how many hubs can be connected to one USB port?

Do they become all confused beyond a certain figure and the whole system crashes?

  Fruit Bat /\0/\ 17:53 23 Dec 04

122

That's theoretically how many devices can be daisy chained off one port.

In pratice the answer is different 1 port can only supply something like 500mA. So once that is raech then the port will be overloaded.

Typically a BB modem or a USB printer takes this amount of current. So only the one device can be plugged in.

  Diemmess 18:19 23 Dec 04

We are both saying the same thing really. I was aware of power consumption limits....... The figure of 122 does surprise me, even though it is only a theoretical maximum.

I suppose that possible difficulties with pecking order and recognising individual devices, was more in my mind, than reality.

  Fruit Bat /\0/\ 18:39 23 Dec 04

Lots of USB info on these sites:

USBMAN
click here

USB FAQ
click here

  Diemmess 19:11 23 Dec 04

Thanks

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