I need to forewarn you: this will get confusing. And it’s entirely the fault of the USB Implementators Forum (USB-IF), so don’t blame me ;).

First, a refresher on the release cycles leading up to USB 3.0:

1996: USB 1.0 (up to 1.5 Mbit/s or 12 Mbit/s)

USB 1.0 (up to 1.5 Mbit/s or 12 Mbit/s) 1998: USB 1.1 (up to 12 Mbit/s)

USB 1.1 (up to 12 Mbit/s) 2000: USB 2.0 (up to 480 Mbit/s)

USB 2.0 (up to 480 Mbit/s) 2008: USB 3.0 (up to 5 Gbit/s)

So far, quite easy, right? USB 2.0 introduced speeds of up to 480 Mbit/s (compared with up to 12 Mbit/s with USB 1.1).

You can use USB 1.0 and USB 1.1 devices on a USB 2.0 port at their lower nominal speed. With the introduction of USB 3.0, backwards compatibility for USB 1.x was dropped.

In 2013, USB 3.1 was introduced which preserved the speeds provided by USB 3.0 (which is often marketed as SuperSpeed) and introduced a faster speed marketed as SuperSpeed+ with a transfer rate of up to 10 Gbit/s.

Unfortunately, the USB Implementators Forum decided to brand SuperSpeed (which is part of the older USB 3.0 specification) as USB 3.1 Gen 1, and the new SuperSpeed+ transfer mode as USB 3.1 Gen 2.

USB 3.0 (SuperSpeed): Now called USB 3.1 Gen 1 (up to 5 Gbit/s)

Now called USB 3.1 Gen 1 (up to 5 Gbit/s) USB 3.1 (SuperSpeed+): Now called USB 3.1 Gen 2 (up to 10 Gbit/s)

So now, SuperSpeed and SuperSpeed+ is now technically a USB 3.1 standard, despite the fact SuperSpeed was introduced with USB 3.0.

But it gets even more confusing.

With the introduction of USB 3.2 in 2017, the USB Implementators Forum preserved the transfer modes provided by USB 3.0 SuperSpeed (up to 5 Gbit/s) and USB 3.1 SuperSpeed+ (up to 10 Gbit/s), and introduced a new transfer mode of up to 20 Gbit/s.

In their wisdom, they also decided to retroactively rename the USB 3.1 Gen 1 and USB 3.1 Gen 2 transfer modes:

USB 3.1 Gen 1: Now called USB 3.2 Gen 1 (up to 5 Gbit/s)

Now called USB 3.2 Gen 1 (up to 5 Gbit/s) USB 3.1 Gen 2: Now called USB 3.2 Gen 2 (up to 10 Gbit/s)

What about the new 20 Gbit/s transfer mode, you ask? That’s called USB 3.2 Gen 2 x 2, of course. You knew that, right?

To summarise, the standard is now as follows:

USB 3.2 Gen 1: Originally USB 3.0 SuperSpeed, up to 5 Gbit/s

Originally USB 3.0 SuperSpeed, up to 5 Gbit/s USB 3.2 Gen 2: Originally USB 3.1 SuperSpeed+, up to 10 Gbit/s

Originally USB 3.1 SuperSpeed+, up to 10 Gbit/s USB 3.2 Gen 2 x 2: Introduced with USB 3.2, up to 20 Gbit/s [1]

Yes, USB 3.2 Gen 1 used to be called USB 3.1 Gen 1 which used to be called USB 3.0. Furthermore, USB 3.2 Gen 2 used to be called USB 3.1 Gen 2 despite being the only new transfer mode introduced with USB 3.1.

[1] Please note the USB 3.2 Gen 2 x 2 transfer mode is only supported via the USB-C connector.

USB-C ports

What confuses users the most about USB 3 is the introduction of USB-C. It is first important to clarify that USB-C is not another standard that competes with USB: it’s actually a connector design that Thunderbolt 3 also shares.

Not all USB-C ports are the same: it is important to check which USB 3.2 standard it supports — if the manufacturer says the USB-C port supports USB 3.1 Gen 1, then it supports USB 3.2 Gen 1 which supports speeds of up to 5 Gbit/s.

As previously stated, USB 3.2 Gen 2 x 2 (up to 20 Gbit/s) is only supported via the USB-C connector.

Thunderbolt 3 ports

It turns out, a Thunderbolt 3 port can also be used to power USB-C devices because it also has support for USB 3.2 Gen 2 (up to 10 Gbit/s).

When Thunderbolt 3 was originally introduced, USB 3.2 didn’t exist and it was marketed as also supporting USB 3.1 Gen 2, but as we’ve already established, this is now called USB 3.2 Gen 2.

If you use a Thunderbolt 3 device in a host machine with the same port, you can enjoy speeds of up to 40 Gbit/s. However, you won’t get speeds above 20 Gbit/s unless the cable you are using is less than 0.5m. With longer cables, they need to be active (instead of passive) to achieve speeds of up to 40 Gbit/s.

Despite the fact Thunderbolt 3 shares the USB-C connector design, you cannot use Thunderbolt 3 devices on computers with only USB-C ports which are not actually Thunderbolt 3 ports.

About me

My name is Ben Stones. I lead Sprint Boards®, an online retrospective tool for Agile developers, providing distributed teams with the tools they need to discuss and collaborate together from anywhere.