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What is a USB root hub?

My computer shows three USB Root Hubs in Device Manager.

The first USB root hubs show four ports, the second shows three ports and the third shows eight ports are available.

However my computer has a total of eight USB ports. Four ports are at the back of the cabinet and four at the front.

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Enhanced USB controller shows 8 Ports are available. Even then when i connect some USB devices to my computer it shows, " This devices can perform faster if connected to Hi-Speed port " . –  Torpido Jul 19 '11 at 13:09
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3 Answers

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Are your USB ports USB 2.0?

It is a common design for USB 2.0 ports to be managed by two controllers: one for low speed and full speed (the USB 1.1 speeds), and one for high speed (the new speed available beginning with USB 2.0). If this is the case, the 3rd root hub is probably from the EHCI controller managing the high speed connections, and the 1st and 2nd root hubs are probably from a pair of OHCI or UHCI controllers managing the low and full speed connections. Each USB port on your computer would then be connected to two of the controllers, the EHCI controller and one of the other two controllers, and which one is used would depend on the speed chosen by the USB device connected to that port.

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I think you are right ........ In USB 2.0 there are 3 chip on Board. 1 chip to controll Hi speed data transfer, and the other 2 are for Low and High speed data transfer. Each controller has 1 USB root hub. So i think you are right in saying that each USB port is controlled by one or more USB controller. Thanks ! –  Torpido Jul 19 '11 at 12:55
    
@Torpido: not 3 chips, but 3 cores within the same chip (probably the southbridge chip in your case). Yes, they look to the operating system as if they were 3 separate chips. –  CesarB Jul 20 '11 at 11:44
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You may have some internal ones if there is a PCI card. If you have a hub plugged in to expand the number of ports, that is there, too. And some device you have plugged in could have additional ports as well.

USBDView and USBView may help you sort out what is where.

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Thanks for the USBView utitlity. –  Torpido Jul 19 '11 at 12:54
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The number of ports displayed in the device manager is dependent on the board architecture. (My laptop has only 4 USB ports, but there are 7 USB Root Hubs in the Device Manager, for example.) And if you see the word "enhanced," it's a safe assumption that the device is virtual, there to satisfy Windows' driver requirements.

Try switching Device Manager to "View devices by connection," for information that makes a little more sense.

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