USB 3.0 ports backwards compatibility problems with 2.0 devices

usb-2usb-3

I see some info on the net that suggest that I should be able to get my USB 2.0 devices to work in 3.0 ports. I only have two 2.0 ports on my new computer, and six 3.0 ports. I have installed drives. There's two different drivers, I guess some of the ports are supported by the intel board and some supported by some other chipset on the motherboard.

I however have yet to get any of the 3.0 ports to work, and my brother had had the same issue with his devices not working in 3.0 ports on his computer. So I am beginning to wonder if the backwards compatibility isn't reliable for some reason. Maybe manufacturers opting not to implement 2.0 support on the 3.0 ports. I understand that physically the wiring is there, but that is only half the story.

Beyond my brother's and my own computers (different motherboards/everything), I have yet to see a 2.0 device work in a 3.0 port. Is there any reason for this apparent device incompatibility? I.e. looking for responses that would indicate what areas to explore for issues or if there is any known cases of manufacturers deviating from spec in hardware or drivers. I am aware it's "supposed" to work 🙂

Update: Does this have any relation to "USB Legacy Support" options in the BIOS? There several options combinations of options with "USB Legacy Support" and "USB 3.0 Legacy Support" and the description for these is a bit confusing, sounds like a bad translation.

Best Answer

From Wikipedia:

Compatibility of USB 3.0 connectors

  • Type A plugs and receptacles from both USB 3.0 and USB 2.0 are designed to interoperate.
  • Type B receptacles in USB 3.0 are somewhat larger than would be required for a Type B plug in USB 2.0 and earlier. This is intended to allow connecting an older Type B plug into a newer USB 3.0 Type B receptacle. Accordingly, a USB 3.0 Type B receptacle on a peripheral device can be connected using the corresponding plug end of a USB 2.0 Type B cable.
  • Type B plugs in USB 3.0 are somewhat larger; therefore, a USB 3.0 Type B plug cannot enter a USB 2.0 or earlier Type B receptacle. Accordingly, normal USB 3.0 Type B plugs cannot be inserted into normal USB 2.0 Type B receptacles found on peripheral devices (and connect them to a computer).
  • A receptacle for eSATAp (eSATA/USB Combo) is designed to accept USB Type A plugs from USB 2.0 and USB 3.0.

In theory, there should not be a problem at the hardware level. However, there may be a problem with the drivers or the underlying controller for the ports.

To determine if this is a hardware or software problem, try booting into a Linux live CD and see if USB 2.0 devices work in the USB 3.0 ports. If they do work, the problem is in the drivers. If not, the problem is in the hardware.

Legacy support in the BIOS only applies to systems that do not natively support USB in general. When this setting is enabled, the BIOS attempts to provide a compatibility layer for very old operating systems such as Windows 95 or MS-DOS, so that storage devices attached to these ports can be used (probably with some restrictions such as no hot-plugging). I'm not sure about this, but USB 3.0 legacy support setting is probably to allow USB 3.0 devices on such operating systems to communicate at USB 3.0 speeds. An operating system that supports USB should not be affected by these settings, as they can communicate with the USB hub controllers directly without having to rely on the BIOS.

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