Re: How to understand USB displays in device manager

From: Marc Reinig (Marco_at_newsgroups.nospam)
Date: 03/09/05 

Date: Tue, 8 Mar 2005 16:29:48 -0800

> 1) "USB Root Hub" is displayed to show empty USB ports. When USB device
> is connected to one of these ports, USB peripheral device driver will
> be displayed replacing "USB Root Hub" display because port is now
> connected.

No, "USB Root Hubs" don't disappear, they are devices in themselves. Each
Host Controller will have it's own Root Hub. Each Root Hub represents one
individual USB bus (Universal Serial Bus bus?).

> 2) If (1) is true,

It's not.

> when I connected my GreenHills USB probe, it didnot
> replace any of "USB Root Hub"

It wouldn't, nothing would cause that.

> but instead added a display entry under
> "Universal Serial Bus controllers". Curious, I looked into INF file and
> class=USB.

Class, USB, includes USB host controllers and USB hubs, but not USB
peripherals.

> So I dont understand how to interpret this. Probe is
> definitely a USB peripheral device.
Yes, a hub or host controller are USB devices, but they are also in a
special class as far as setup classes go and thus are treated differently.
The USB in the INF file identifies them as such.

> 3)Are the number of USB ports available for device connection are same
> as "USB Root Hub" displayed? What about controllers?

No, you can have a root hub with several ports. They are all on the same
bus. Devices connected to different root hubs are on different busses.

In device manager, chose View/ Devices by Connection. You'll find the
controllers under ACPI .... /Microsoft ACPI-Compliant system/PCI bus.

Marco
________________________
Marc Reinig
UCO/Lick Observatory
Laboratory for Adaptive Optics

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