The internal operation of USB controller chips is incredibly complex.
For example, take the Intel ICH 5 chip. It has, internally, four
two-port USB 1.x controllers AND one eight-port USB 2.0 controller and
it has external connections for eight USB sockets. But the assignment
of the sockets to the five internal controllers is dynamic, and can
change while the machine is running (e.g. if you unplug a USB 1.x device
from a USB physical port (socket) and plug in a USB 2.0 device (or
vice-versa), the port (socket) can "move" from one controller to
another). Don't try to figure it out, just use it, as long as it is
working.


markus4412@yahoo.co.uk wrote:

> Hi, through Windows XP's device manager, I see I have four 'USB Root
> Hub' devices. These correspond to the four usb ports on my laptop, 3
> on the right of the machine and one on the left.
> When I right click on the devices, and choose 'Properties', I can click
> 'Power' and for each of the right USB hub devices I'm told there are
> '2 ports available'., for the left side one i'm told there are '6 ports
> available'
>
> After fiddling though, it seems that two of the actual external usb
> sockets on the right of my laptop seem to correspond to one of the usb
> hubs - if i put my mouse in one socket, and my bluetooth dongle in the
> one next to it, they both show up on the same 'usb root hub' devices'
> Power page, and there are no more 'ports' available on this one.
>
> The third external usb socket is there on its own, but also supports
> two ports - would I need a hub to access these, or Is there some kind
> of splitting device to turn one socket into two that might be cheaper?
>
> Again with the left-hand external usb socket - this appears to support
> 6 devices (at up to 500ma per device), would I really need a hub for
> this or can I again just get a splitter of some kind?
>
> Finally, there is a fourth 'usb root hub' device listed, but there is
> no physical usb port that corresponds to this; is this just due to the
> generic way some laptops are made and it simply hasn't been connected?
>
> Hope that made sense!
>
> Mark.
>