Understanding USB topology in Windows XP

by Greg Shultz | May 02, 2007 7:00:00 AM

Tags: Greg Shultz, USB, USB Hub, Microsoft Windows XP, Microsoft Windows, Windows XP Tips Newsletter

Takeaway: Ever wonder how many USB devices your Windows XP system can handle? The answer may surprise you. Here's how your machine organizes all its connections and how you can evaluate the Device Manager's total running capacity.

As long as you have enough power, attaching many USB devices to your Windows XP system can't cause degradation in performance -- even if you attach as many as 127 USB devices at one time.

While it's unlikely for that many devices to be connected at a time, that number is made possible by Windows XP's seven-tiered USB topology. The top, or tier number one, consists of the host controller or root hub, which is the USB hub built into the computer's motherboard. Tiers two through six are equipped to consist of a series of USB hubs (two or more at each tier) daisy chained together. Tier seven consists of any devices attached to the USB hub(s) at tier six.

While USB hubs can draw power from the root hub, the amount of power is limited to 100 milliamperes per port, and the hub can only have four ports. However, most USB hubs have their own external AC adapter and can provide up to 500 milliamperes of power per port on more than four ports.

Follow these steps to learn more about the root hub and the USB hubs attached to your system in Device Manager:

1. Go to Start, right-click My Computer, and select Manage.
2. Click Device Manager in the left pane.
3. Click Universal Serial Bus Controllers in Device Manager.
4. Double-click each root and USB hub and check the information on the tabs.

Note: This tip applies to both Windows XP Home and Windows XP Professional.

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Print/View all Posts Comments on this article

Loading USB device drivers on multiple ports.JK9489  | 05/04/07

You may need an expertblarman  | 05/04/07

Windows port control is flawedTexNex  | 05/04/07

Number of devices is per root hubpeter.j.boyles@...  | 05/04/07

ClarificationJK9489  | 05/04/07

Color codingGreg Shultz  | 05/04/07

USB Powered HubAydin H  | 05/20/07

identification of USB portsjosef.kaiser@...  | 07/23/07

Identification of USB Portsrailroads@...  | 08/09/07

RE: Understanding USB topology in Windows XPgls0927@...  | 07/19/07