Powered USB hubs

[mopeygoth]

Dear all,

I surfed the boards for some time now and did not find a specific answer (always get caught up at some irrelevant question =) ).

we (girlfriend and I) both own usb hubs. Same model with a powersupply adapter to follow. Thing is that all devices (usb-cam, usb-scanner, usb-mouse, usb-keyboard) work fine without the powersupply for the hub. I have left it unpowered and it lights and sparks as it shall =).

Is the hub-powersupply intended for un-self-powered usbdevices? Is it for a chain-link of usb-hubs to maintain speed and bandwidth? Or..?

Another question:
Will the total bandwidth of the motherboard's usbports be shared to all ports or only for the ports where there are coonections?
(e.g. 12 ports sharing 12mbps with a portspeed@1.0mbps. or 10 "inactive" ports and two ports active (with connectors; e.g. usb-hub, usb-scanner) with a portspeed@6mbps.

Thanks a lot...!

Intel Pentium 4 - 400Mhz FSB - 2.4Ghz
- 1152mb pc-133 - Ati Radeon 9700 128Mb

 

[sturm]

Powered hubs are needed if you have a lot of non-powered devices: i.e mice keyboards, usb floppy, some scanners, cameras, and such. The usb will onlysupply so many volts and amps to the usb line so you need to make sure that you dont over do it.
As far as the bandwith, each device will use all the bandwith available to use. If only one device is sending data then it will transfer faster than if 3 or 4 are trying to transfer all at once.
The hub justs splits the signal to all ports just like in a network hub. Only the device that needs the info will accept it.

 

[mopeygoth]

so, there will be no performance issue by powering the hub?

Scanner 496mA
MouseMan Wheel 100mA
sightCam 100mA

Thanks for replying

Intel Pentium 4 - 400Mhz FSB - 2.4Ghz
- 1152mb pc-133 - Ati Radeon 9700 128Mb

 

[upec]

The power supply allow usb hub to provide upto 500mA on each port. You should use the power supply for the USB hub since without power supply each device should only draw less than 100mA from the port.

 

[mopeygoth]

well... windows state that the scanner uses 496mA, is that then just an estimate of what it "needs" and not what it actually uses?

Intel Pentium 4 - 400Mhz FSB - 2.4Ghz
- 1152mb pc-133 - Ati Radeon 9700 128Mb