En continuant mes recherches j'ai trouvé sur le site
http://www.intel.com/content/www/us/en/support/boards-and-kits/000005506.html
l'information suivante :
The Intel® USB 3.0 eXtensible Host Controller Driver is not supported in Windows* XP or Windows* Vista. For these operating systems, make sure your BIOS settings have the xHCI Mode set to Auto or Smart Auto. This step reconfigures the USB 3.0 ports to function as USB 2.0 ports using the native Windows* EHCI driver.
J'ai aussi trouvé sur un forum :
XHCI Mode = Disabled - The on-board USB 3.0 port function like a 2.0 port
XHCI Mode = Enabled - The on-board USB 3.0 port function like a 3.0 port
XHCI Mode = Auto - The on-board USB 3.0 port function like a 2.0 port before OS USB 3.0 driver load. If you reboot the OS, the on-board USB 3.0 port again function like a 2.0 port during this reboot BIOS phase before OS USB 3.0 driver load.
XHCI Mode = Smart Auto - The on-board USB 3.0 port function like a 2.0 port before OS USB 3.0 driver load. If you reboot the OS, during this reboot BIOS phase, BIOS is "Smart" enough to avoid downgrade the USB 3.0 port back to 2.0 functionality before OS USB 3.0 driver load. So Smart Auto is faster than Auto on 2nd boot onward, but Enabled is fastest once you are sure the OS has the USB 3.0 driver installed, because it avoid the switching. Making the on-board USB 3.0 port function like a 2.0 port is mainly to support OS installation or to support OS that does not have build-in USB 3.0 driver, so that the USB keyboard would still work if the user plug-in a USB keyboard or any other USB devices into the USB 3.0 ports before the OS is installed with the USB 3.0 driver come with the motherboard.
J'en conclus que, si on peut agir sur le paramètre XHCI Mode (via le BIOS je pense), un périphérique USB3 branché sur un port USB3 sera vu comme un périphérique USB2 par XP ou VISTA. Dans le cas contraire il faudra impérativement se brancher sur un port USB2 (ce qui est mon cas).
