DisplayPort backwards compatibility dwarfs USB • The Register

The USB Implementers Forum, USB-IF, published the USB 4 Version 2 specification just last month, as you’ve probably read That to register. We noted at the time that the essentials would be released in time for the developer events planned for November.

Well it’s almost November and a more detailed announcement [PDF] is here. (We particularly like these _FINAL_v2 at the end of the file name. We all did.)

If you have a 40Gbps passive USB-C cable, it seems it can now do 80Gbps with USB-4 v2. Good for you if you know the speed rating of your USB-C cables because here at the Registration number FOSS Desk, we freely admit that we don’t. We don’t even know if ours are active or passive. We can only apologize for this pathetic lack of professionalism and once we learn how to recognize this we will put a new cartridge in our label printer and fix this.

Compare this to the Video Electronics Standards Association’s announcement of DisplayPort 2.1, which notes:

So if you have a DisplayPort 2 kit, relax because it still works fine with the DP2.1 kit as it should.

USB-4 v2 will also include next-generation Thunderbolt.

Forget about using older Thunderbolt devices on Thunderbolt 4 ports, though. They don’t work as described in this note halfway down the official Thunderbolt FAQ:

Even if you buy a Thunderbolt 1 or 2 to Thunderbolt 3 adapter, it won’t work with modern Intel kits:

Yes, Intel has quietly dropped backwards compatibility with the 10th Gen Core chips. Thunderbolt unfortunately adds additional functionality to your USB-C port, but it doesn’t work from one generation to the next, which is what generally characterizes USB, for all its vicissitudes.

This is unsupported by issues like Dell firmware updates breaking Thunderbolt support, as reported time and time again on the company’s support forums.

USB-C is a mess, as noted in 2018 and 2020, and it still is in 2022. Unfortunately it’s the best we have. ®

bootnote

In case you have DisplayPort to HDMI cables nearby, a handy tip from the Registration number FOSS desk: They are disposable. You can connect any HDMI display to a Displayport connector, but you tip Connect a Displayport display to an HDMI port. (There are adapters, but they are not cheap and relatively bulky, active devices, so cheap cables will not do.)

In contrast, HDMI to DVI works both ways: not only can you connect a new HDMI display to a computer with the old DVI connector, you can connect an old display with DVI to a new computer that only has HDMI , e.g. a Raspberry Pi.

https://www.theregister.com/2022/10/20/displayport_revision_usb/ DisplayPort backwards compatibility dwarfs USB • The Register

Rick Schindler

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