USB4 will be formally published at the USB Developer Days Seattle on September 17, and the USB Implementers Forum (USB-IF) is expected to continue the widely maligned naming scheme for USB speeds introduced in February for USB 3.2, an engineer familiar with the USB-IF’s plans told TechRepublic.

As a quick recap, USB 3.1 Gen 2, increased the lane speed to 10 Gbps. A second 10 Gbps lane was added in the USB 3.2 standard, which the USB-IF calls “USB 3.2 Gen 2×2.” USB4 (which is not written as “USB 4.0”) will reach speeds of 40 Gbps, doubling the speeds again. USB4 was first previewed in March, when the USB Promoter Group announced that USB4 would be based on Intel’s Thunderbolt 3 specification, though specific details are expected later this month.

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“Once the specifications are released, there will be a new round of confusion,” the source told TechRepublic. “It’s going to be USB4, but you have to qualify what USB4 means, because there are different grades. USB4, by definition, has to be [at least] Gen 2×2, so it will give you 10 Gbps by 2, that’s 20 Gbps. There’s going to be USB4 Gen 3×2, which is 20 Gbps per lane. 20 by 2 will give you 40 Gbps.”

In what universe does the USB naming convention make sense?

The branding policy of the USB-IF is an apparent war against common sense, as new versions retroactively rename previously published standards, leading to widespread confusion among consumers.

The USB-IF’s branding guidelines for USB 3.0 have created a great deal of confusion. When USB 3.1 was released, the 5 Gbps USB 3.0 was retroactively renamed “USB 3.1 Gen 1,” with the new 10 Gbps mode called “USB 3.1 Gen 2.” This happened again with the release of USB 3.2. With the 20 Gbps mode-which uses USB Alternate Mode to provide a second 10 Gbps lane, the new standard was named USB 3.2 Gen 2×2. The other standards were incremented to USB 3.2 in name only, as detailed in the chart below.

Generation Previous name New name Speed Type
USB 3.0 USB 3.1 Gen 1 USB 3.2 Gen 1 5Gbps USB-A/C
USB 3.1 USB 3.1 Gen 2 USB 3.2 Gen 2 10Gbps USB-A/C
USB 3.2 None USB 3.2 Gen 2×2 20Gbps USB-C

Why would I want USB4, and when can I buy a computer with it?

Thunderbolt 3—upon which USB4 is based—supports PCIe 3.0 and DisplayPort 1.2 signaling, making it capable of driving 4K monitors at 60Hz, as well as external desktop-class GPUs that can be used to bolster the graphical capabilities of notebook PCs and small form factor devices like the Mac Mini. USB4 will also inherit the ability to deliver up to 100W of power.

Because Thunderbolt 3 is already a known quantity for engineering teams, the time-to-market for USB4 should be modestly faster than a completely new standard. However, maintaining a 40 Gbps transfer rate with Thunderbolt 3 is complex, as this requires “active” cables with circuitry in the connectors for cables longer than 50 cm (1.5 ft).

For more, check out “Speed-doubling USB4 is ready. Now we just have to wait for devices” at CNET.


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