Igor Bubelov About Blog Photos

Thunderbolt 4 and USB 4

January 13, 2020

Thunderbolt 3 is an interface that is available on pretty much every high-end laptop nowadays. It’s almost too good to be true. Thunderbolt-enabled hardware have a set of unified USB ports that can be connected to up to four PCIe 3.0 lanes. One such lane gives us up to 8 GT/s (985 MB/s), so it should give us up to 32 GT/s, although Intel claims that it’s capable of 40 GT/s. I’m not sure where those extra 8 GT/s come from, but many people claim that their Thunderbolt 3 devices are only capable of ~22 GT/s. Anyway, it’s crazy fast!

Fast transfer speed is not the only benefit of Thunderbolt 3, it also allows us to charge our devices or send video output to external monitors. It’s also possible to use an external GPU and even Ethernet over Thunderbolt. Think of a small GPU enclosure that you can connect to your laptop with a single USB cable and aside from being able to do many GPU-intensive tasks, it would also keep your laptop charged and route your traffic via a wired interface which may improve your network throughput and latency. It’s a truly amazing little port.

So, on CES 2020 keynote, Intel announced a new generation of Thunderbolt: Thunderbolt 4, which left many people excited and confused at the same time. Intel promised some speed improvements, so it’s supposed to be 4 times faster than… USB 3.2. 2x1. Well, that was unexpected. Why do they compare Thunderbolt 4 to USB when they have Thunderbolt 3 as a more clear point of reference? They announced that Thunderbolt 4 is 4 times faster than USB 3.2. 2x1, which means 40 GT/s, same speed as Thunderbolt 3. That’s very strange, maybe they’ll clarify things later.

Aside from Thunderbolt standards, now we also have USB4 out in the wild. It’s practically the same thing as Thunderbolt 3, nothing new and exciting, but at least it’s not semi-proprietary which is nice. It looks like we’re going to stick with 40 GT/s for a while.

Actually, I expected that Intel would use the full potential of PCIe 4.0 which doubles the bandwidth to 16 GT/s (1970 MB/s) per every lane. A man can dream.