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Glendale, AZ

USB 3 not 100% compatible with USB 2?

I have an Asus laptop with USB 3 for one of the ports. Have a couple of USB 2 devices that will not work. Thought the port was bad. It was sent in for repairs under warranty. Tech checked it out. USB 3 devices working properly on that port. Some USB 2 working as well as he tested. Tech said there are some USB 2 devices that are not working with USB 3 ports. Mostly a trial and error thing.

I thought it was 100% backwards compatible?

Bloom County
In USB 3.0 dual-bus architecture is used to allow both USB 2.0 (HIGH Speed/LOW Speed/FULL Speed) and USB 3.0 (Super Speed) operations to take place simultaneously, thus providing backward compatibility. Connections are such that they also permit forward compatibility, that is, run USB 3 devices on USB 2.0 ports. The structural topology is the same, consisting of a tiered star topology with a root hub at level 0 and hubs at lower levels to provide bus connectivity to devices.

It is backward compatibility but it looks like, from what the tech said, there are some devices that have issues being plugged into USB3 port. Likely in the drivers device uses. Don't think it is a USB3 implementation issue but specific hardware with drivers not coded correctly.

"It drops into your stomach like a Abrams's tank.... driven by Rosanne Barr..." A. Bourdain

Saint Paul, MN
reply to jsmiddleton4
said by jsmiddleton4:

I thought it was 100% backwards compatible?

It is...except when it doesn't work. You don't mention how you're using these. I have issues booting from a USB3 device. If I plug the same device in a USB2 port it boots fine. Once inside of Win7 it works fine on any port.

Like almost everything else in life, your mileage may vary.
When will the people realize that with DRM they aren't purchasing anything?

Mountain View, CA

2 recommendations

Booting from USB 3.x devices may be problematic given the implementation details of USB 3.x support on some boards. Let me explain in detail:

For example, on my Gigabyte GA-P67A-UD3-B3 there is a Renesas (NEC) USB 3.0 controller associated with 2 ports on the backplane. You cannot boot off of these ports, for what (to me anyway) is quite obvious: it's a third-party chip, the BIOS would need full emulation shims and a BIOS-level driver (code) to talk to the underlying Renesas controller and provide the necessary tie-in shims. It's a lot of work, and not feasible. These chips do not provide xHCI (keep reading) to my knowledge.

I also have a Renesas (NEC) USB 3.0 PCIe x1 controller (physical card) in my system too, which provides another 2 ports (this time wired to the front panel of my case). One cannot boot off of these ports either -- to do this, one would need an option ROM, which the card does not have. Furthermore, option ROMs often do not "stack" well. (Example: a system with AHCI enabled + a SCSI controller + PXE network boot all enabled probably won't work, but it depends completely/entirely on the motherboard) These cards also do not provide xHCI.

Expanding even further: the newest/latest Intel chipset boards (e.g. Z77, etc.) provide native USB 3.x support, except the implementation there is something I haven't even begun to read up on yet. The newest fun thing is called xHCI (not to be confused with OHCI, UHCI, and EHCI -- all of which are described here), and systems that use xHCI provide a multitude (literally 6 or 7 options; download the User Manual and see the BIOS section) pertaining to booting xHCI devices (whether they be USB 3.0, 2.0, 1.1, or 1.0).

Thus, with xHCI, USB 3.0 devices will use xHCI, USB 2.0 devices will use the EHCI capability (despite attached to an xHCI controller), and USB 1.1 and 1.0 will use UHCI. This is exactly how the existing USB 2.0 model works, and how/why the USB ports are all "universal" in capability. I will note that there were some early USB 2.0 adopter motherboards which had separate USB 2.0 and USB 1.1/1.0 capable ports, which was very strange but did exist. This is not the norm these days; a USB port is a USB port.

The downside to xHCI is that Intel, for whatever reason, is refusing to provide Windows XP drivers for it, citing that "it only works on Windows 7", and as such you can only achieve up to USB 2.0 speeds with xHCI controllers on Windows XP. This affects people like me greatly since I refuse to go to Windows 7 for reasons I also refuse to get into here.

My point is that the reason you can't boot from your USB 3.0 devices is probably because of my 2nd paragraph above. That has nothing to do with "device compatibility" (specifically USB 2.0 devices not working on USB 3.0 ports), it has to do with how PC architecture is poorly designed. Then comes the whole UEFI/EFI thing which I don't want to get into either...

Footnote: isn't it great how USB stands for Universal Serial Bus, except there's 1. nothing universal about it (nobody seems to think ahead when designing these protocols), and 2. absolutely no USB standard/classification for serial ports? Welcome to what committees do these days -- very little.
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.

·Verizon Wireless..
reply to jsmiddleton4
It should be. If these are devices with cables, and not something like a flash drive, then you might try a different cable.

USB 3.0 is slightly deeper and some usb 2.0 connectors don't seem to make proper contact with the usb 2.0 compliant pins in the connector. Sometimes if you fiddle with it you might get a momentary connection.


Markham, ON
reply to jsmiddleton4
Most likely your laptop will be using a Renesas (NEC) USB 3.0 controller. I would try to check if the drivers are up to date from your laptop manufacture website. If that doesn't work check if there is any option in the BIOS to get it working.

·Cogeco Cable
reply to jsmiddleton4
I can confirm that some devices have issues. It's random.

I have a PS/2 keyboard & Mouse to USB adapter I use with a KVM switch and it works great with USB1 / USB2 PC's, but it intermittently causes erratic behaviours when I use a Renasas chipset based USB3 port.

Hard drives seem to be okay.