Explaining 4K 60Hz Video Through USB-C Hub

Oh you sweet summer child. If you want to buy a laptop these days, you have to shell out 300$ for what is basically half of the motherboard and connect it externally over USB-C.

So many wrongs in this article.

> To keep a 60 Hz refresh rate, you need to step down to 2K or lower resolution.

Nope. 3440 x 1440 @ 60Hz is the highest res currently used which still fits half the bandwidth of DP 1.2, see here: https://linustechtips.com/main/topic/729232-guide-to-display...

> They are very likely DisplayPort Alternate Mode designs using four lanes.

If a hub claims to support 4K @ 60Hz and USB 3.0 it doesn't necessarily mean it supports both at the same time. It can be convenient to have a flexible hub which, when connected to a monitor where two lanes are enough then USB 3.0 is provided, if you go above then it slows down to USB 2.0. At least one of the hubs linked from the article (very small with one power, one USB 3, one HDMI and a non-captive cable) is such, this was confirmed by one of the sellers, this device is available with many, many labels.

The article also omits that many, many notebooks with a single Thunderbolt 3 port will not support multiple 4K @ 60Hz because they put only four DisplayPort lanes in there using a cheaper, lower power controller called the Alpine Ridge LP. And yes, that pos is still in use despite I hoped Titan Ridge will deprecate it. Dual port Thunderbolt controllers are all full bandwidth, single can be half or full. Hard to tell without looking up the TB controller used in the device on social media / stackexchange etc -- the manufacturers are often quite tight lipped on the topic.

Another fun fact: while the Thunderbolt 3 bus is indeed 40gbps, that's only filled out when video is used, the data speed is nerfed to 22gbps by all existing controllers. Dell admits this in one article https://www.dell.com/support/article/us/en/19/sln307875/thun...

> Thunderbolt 3 may only reach a maximum data transfer rate of around 7 to 22Gbps even though it is advertised with 40Gbps

but this is so rare, every other article, even the one linked from this rare gem of truth claims some baloney like "Systems with 4 lane design will support up to 40gbps of data transfer over PCIe" which is obviously not true because even without nerfing PCIe 3.0 x4 is 32gbps only but it is nerfed. The official TB3 brief also tells you this but a little overt because it is never stated in the text but Figure 7 shows what's up in https://thunderbolttechnology.net/sites/default/files/Thunde... And make no mistake, there are only PCIe and DisplayPort signals on the TB3 bus, there are no USB signals, the TB3 controller in the dock provides a USB root hub. Someone should bring a class action lawsuit to Intel and practically all laptop makers for false advertising in this... (Side note: USB 4 will be different in the signals, if my understanding is correct then the Thunderbolt 3-like bus which is an optional mode for USB 4 will finally contain PCIe, DP and USB signals.)

I have written similar explanations in the past for eg https://www.reddit.com/r/thinkpad/wiki/newdocks https://superuser.com/a/1200112/41259

The USB-C spec is an insane mess.

The fact that every port used to be different is actually a feature, as it helps you identify which device supports what based on the ports it had. If you see an HDMI port on a laptop you can be sure it's going to output some kind of video signal over that. If you see Thunderbolt then you're sure the machine supports Thunderbolt.

USB-C just jams all these incompatible standards into a pin-count-constrained port (so they can't even all fit in, and trade-offs need to be made) without any way for the user to tell nor select which features should be enabled on which port.

My 12-inch MacBook for example has a USB-C port just like the MacBook Air and Pro, and yet if I plug in a Thunderbolt Display it won't work on the 12-inch one but will on the Air and Pro. As a user there is no easy way for me to tell the 12-inch Macbook's USB-C port is different than the Air/Pro unless you explicitly search for it in the tech specs (which is counter-intuitive as the whole point of USB-C is to be universal so in an ideal world you wouldn't/shouldn't even think about searching that).

> Unlike most alt-mode; this will also remap A7, A6, B6, B7 to carry USB 3.0 signal, instead of the usual passive USB 2.0 signal. This means that one will not be able to extend the cable using a standard USB-C 3.0 cable, which has these pins mapped only for unshielded USB 2.0 signals. Also this will require the VirtualLink port to also detect the correct orientation of the USB-C plug to ensure that the USB 3.0 TX and RX lanes are correctly connected.

A fun/interesting hack! But breaking superposition is a huge dealbreaker. Imagine seeing notices in software saying to flip your cable upside down...

That's just bullshit. You can check for how many uses a usbc plug was designed and tested for.