3.2 Gen 2x2 (and the occasionally relevant 1x2 if you have a weak cable) are USB C only.
USB C ports and cables have 4 USB 3 "superspeed" lanes rather than two. When you use an A to C cable only one pair of those connects. The point of the "x2" modes is that they use the second pair of lanes that would otherwise go unused.
Except of course they don't always go unused. DisplayPort Alternate Mode sends DisplayPort over those two "unused" lanes getting you USB 3 data alongside a half speed DisplayPort connection. (or alternatively full speed DisplayPort on all four and only USB 2), and then of course Thunderbolt 3 and modern USB4/TBT4 use all four lanes and tunnel everything.
Thank you for answering a question I didn't know I had
The main application of 20 Gb/s USB ports is to connect external NVMe SSDs, when faster USB 4 or Thunderbolt ports and SSDs are not available.
For an external NVMe SSD on USB, a 20 Gb/s USB port will double the throughput, unlike for a 10 Gb/s Ethernet interface where any improvements are completely negligible.
I do not think that 20 Gb/s USB Type C ports are "very rarely supported". Every mini-PC or desktop motherboard that I have bought during the last 10 years had at least one such USB port.
Such ports appear to be rare only on laptops, because most laptops have very few USB ports.
While this may be theoretically (almost) possible, I’m quite sure this is absolutely not the case in practice.
For example see these benchmarks of one of the more recent USB to Ethernet chipsets [1], that can reach ~9.5 Gb/s on USB 3.2 Gen 2x2 but only between ~6.2 to ~7.3 on 3.2 Gen 2x1 laptops.
1. https://www.jeffgeerling.com/blog/2026/new-10-gbe-usb-adapte...
Edit: Haha, didn’t realise TFA was by the same author as these benchmarks but he’s done a lot of testing and benchmarking of these kind of devices over a long time, and it agrees with all the other benchmarking from other people I’ve seen too!
In USB 3.2 Gen 2x1, the actual USB packet throughput is 9.697 Gbps and the "10 Gbps" refers to the raw encoding rate.
This difference means you are guaranteed to lose at least a few hundred Mbps off maximum performance. It's not really a practical concern, but it's not an error to say 10 Gb/s USB ports lack the bandwidth needed to support the maximum performance of a 10 Gbps USB Ethernet adapter.
> The main problem is USB-C's bandwidth complexity - especially when paired with the Realtek RTL8159 Ethernet controller, which requires USB 3.2 Gen 2x2 (20 Gbps) to get the full rated 10 Gbps speeds
Jeff's statement wasn't that 10 Gb/s Ethernet requires 2x2. It's that that requirement comes from a very specific controller.
Are you talking about USB 3.2 Gen 2x2 though? Because I've never seen any MiniPC with this port and as for motherboards, I checked my local retailer and only ~15% of currently sold ones have Gen 2x2 (mostly high-end ones).
With mini-PCs, I frequently use external SSDs, so I certainly used those ports at their full speed.
The only mini-PCs that I had in recent years without such a fast USB port were Arm-CPU based, as those are typically starved in fast peripheral interfaces in comparison with the Intel/AMD CPUs.
The first half is true, the second half is not. Remember overhead. You don't need 20GB/sec, but you need to take into account the USB overhead.
I am of the opinion that 5Gbe is a much more sensible speed for a laptop adapter right now as it uses half the power and can obviously run full wack on 10Gb/s USB so you're looking at like 5Gbe vs ~9.4Gbe.
At distances where Cat.6A is even an option the demands on the fiber are very low. And it uses less power than the BASE-T PHY. The cable at least without integrated power is very thin as well, unless you can't respect it enough to not kink it, in which case you'd want a thicker one just to prevent you from being able to break the fiber.
And you get much better future proofing with SMF. And if you do need a long fast run, SMF is what you want.
So the their maximum speed is approximately 9.7 Gb/s.
Then for Ethernet there is a protocol-dependent overhead, e.c. depending on whether TCP or UDP is used, and depending on whether standard packets or jumbo packets are used.
The TCP overhead can reach in the worst case up to close to another 3%, reducing the achievable TCP throughput to around 9.4 Gb/s.
The USB frames add some extra overhead, but it is normally not important in comparison with other factors that can reduce the throughput.
All that a 20 Gb/s USB port can do is to reduce the overhead of the USB frames, but that is a negligible improvement. Using jumbo Ethernet frames (which are 6 times bigger than standard frames), if both ends support them, is likely more useful for increasing the throughput, than using a 20 Gb/s USB port.