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  • Status: Solved
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Multiple USB root hubs on my PCs

Can someone tell me why all my PCs and laptops have, it appears, far too many USB Root Hubs? What do they do?

Many thanks.
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Peborgh
Asked:
Peborgh
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1 Solution
 
Gary CaseRetiredCommented:
They don't have "far too many USB Root Hubs" ==> they simply enumerate a hub for each of the USB ports (some of which may be internal headers that don't have actual external connectors).
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PeborghAuthor Commented:
Thanks! What do the internal headers do?

peter
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Gary CaseRetiredCommented:
Most motherboards have one or two internal headers that support 2 ports each.   These are used for front panel USB connections;  internal USB devices (e.g. card readers); or can be used for additional external ports via a rear panel bracket (e.g. one of these:  http://www.pcconnection.com/IPA/Shop/Product/Detail.htm?sku=9067922 )
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PeborghAuthor Commented:
Very interesting/helpful, garycase.
Last question - I have never got into the mechanism of how USB works - can you point me to an article that explains this, for the benefit of a software guy, not a hardware person?

peter
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Gary CaseRetiredCommented:
USB 2.0 is essentially a high speed isochronous communications link.   This document has a good overview of the control registers and are used to manage the interface:
http://www.intel.com/technology/usb/download/ehci-r10.pdf
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