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I have a BIOS setting called XHCI Pre-Boot Mode. If I have this enabled USB devices which aren't plugged in at boot are never recognised, if I set it to Disabled then USB devices work normally. The brief BIOS description says "Enable this option if you need USB3.0 support in DOS." Which I don't, but it also says "Please note that XHCI controller will be disabled if you set this item as Disabled." So does that mean that USB3 is disabled with this option? Here's a picture of the screen:

Asus UX32VD Advanced USB BIOS screen

UPDATE I subsequent BIOS update seems to have fixed this issue in that USB devices work even when not plugged in at boot with this option Enabled.

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2 Answers 2

The XHCI controller (Extensible Host Controller Interface) is the USB 3.0 controller. For all practical purposes, you can consider the terms synonymous. So, yes, it sounds like this will disable the controller and the associated ports entirely (unlike earlier controllers, the same stack handles USB1 and USB2 as well as USB3, so this is probably an all-or-nothing prospect).

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But setting it to Disabled allows my USB devices to work normally, so it doesn't disable the ports entirely. –  Jamie Kitson Sep 26 '12 at 21:36
Oh, I read that backwards...but I'd suspect it's actually written backwards then. I'd expect that this option should be off for normal operation. That is to say, leave it disabled. –  Shinrai Sep 26 '12 at 21:39

xHCI Pre-Boot Driver

Enabled The USB 3.0 ports are routed to the xHCI controller before booting to OS. (Default)

Disabled The USB 3.0 ports are routed to the EHCI controller before booting to OS.

When this item is set to Enabled, the xHCI Mode below will be automatically set to Smart Auto; when this item is set to Disabled, the xHCI Mode below will be automatically set to Auto.

source: http://mbforum.gigabyte.de/index.php?page=Thread&threadID=6484

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Some clarification: xHCI is the USB 3.0 controller, and EHCI is the USB 2.0 controller. Possibly (I don't have a system with such options) - if you boot into a rescue environment like Windows PE, and you didn't include USB 3.0 drivers on the CD, things like external drives won't work when you connect them to the ports, UNLESS you set it to EHCI. –  ultrasawblade Jul 21 '13 at 14:54

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