The Specification Is Ready
That Thunderbolt comparison isn’t a coincidence. Intel contributed the Thunderbolt protocol specification to the USB Promoter Group. (The Promoter Group is an industry organization charged with developing USB specifications, while the USB-IF advocates for the advancement and adoption of USB technology.)
When USB4 ports start showing up in laptops and elsewhere, it promises maximum speeds of 40 Gigabits per second (Gbps). That’s double the maximum of current USB 3.2 Gen 2×2. As with other versions of USB, USB4 will be backward compatible with USB 2.0 and up, and in some cases, those USB4 ports will even work with Thunderbolt 3 gear.
Unfortunately, Thunderbolt 3 isn’t mandatory. Some USB4 devices may omit it.
It sounds like a pretty good upgrade, but if there’s anything we can say about the people behind USB, it’s that they sure know how to confuse everyone. USB4 may be no different. Let’s dive in.
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Multiple Speeds
USB4 won’t be just one single standard that you can expect to work the same across all devices. Instead, it will come in two different speeds. In addition to the potential for a maximum 40Gbps speed, there’s also a 20Gbps speed. If that wasn’t enough, there’s also a third option of 10Gbps in the USB4 spec. However, the USB-IF told us that this is simply a fallback speed to support backward compatibility. In other words, don’t expect to see USB4 devices limited to that lowest speed.
It’s currently unclear what the two major USB4 speeds will be called when they hit store shelves. Behind the scenes, the 40 Gbps USB4 speed is called Gen 3×2, and the 20 Gbps speed is Gen 2×2. Those are technical terms for device makers and not something for the signage at your local computer store.
The USB-IF says its branding guidelines will be announced in early 2020. At that time, “there will be a focus on clearly indicating performance levels to the general consumer,” according to a USB-IF spokesperson.
That’s good news as it’s confusing enough right now with USB 3.2, which comes in Gen 1 and Gen 2 and Gen 2×2 flavors. Yes, it’s pretty confusing.
Backward Compatibility
As with other versions of USB, this one is backward compatible with its predecessors. Specifically, USB 2.0 and up. That means if you have a USB 2.0 external hard drive for backups, you can still connect it to a USB4 port. To make that work, you’ll need an adapter to go from USB Type-A (standard USB) to USB Type-C, and our imaginary drive will still be limited to the speeds of USB 2.0.
Also, those USB Type-C cables you have right now are probably not going to be good enough for USB4. It will still support the older speeds, but if you want to see that transfer rate increase, you’ll need new cables and new gear.