> > don't think so, despite the name USB IS NOT A BUS it is a 
> tree of point to point links and the ports always seem to 
> stay powered (except when you short them out ;) ).
> 
> I'm not sure about that. I was under the impression that a hub, when
> brought online, was required to power up one port at a time, since the
> newly-powered device gets the unconfigured address and must be
> configured before another device can be brought up. Again: 
> I'm not sure.
> I have the USB specifications, but I haven't read them yet. 
> This is just
> my impression.
> 

I believe that the power switching is handled by the device, and not the
upstream hub/port. When enumerated, devices are required to keep their
power consumption below some threshhold, and they will then communicate
their power needs and wait for the host to calculate a total power budget
before "approving" a higher load. In other words, higher power devices
must get permission from the host before drawing more than a minimal
current amount. They do their own power switching for their own loads.

There are a few different query/reply methods for the host to inquire
about power needs. Windows does not use them all. Some poorly written
USB devices ignore requests that are not used by windows. While writing 
USB drivers for a new OS, I have seen some brands fail to enumerate after
current managment software was added to the USB stack.

Regarding a hub doing the switching.. the two ports on the front of my
Antec Sonata case have their +5Volt and Gnd contacts wired in parallel,
so switching of individual ports at that level is not possible.

I am not an expert. I welcome any corrections to my understanding of
how these things work. All facts are subject to verification. I reserve
the right to be wrong, and to learn from my mistakes.

Lyle

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