Author of the article here—please do tell me more about the Thunderbolt 3 and USB 4 relationship. I used “basically” to hand wave over some of the detail, but would love to know how to dig down on this further. (And I welcome nit picks. Seriously! We just did a couple tweaks. Some folks who buy HDDs said they see 3.0 Micro-B all the time, and that is absolutely true, so we modified a sentence about that.)
I'm leaning a bit on three things:
• The USB-IF says that USB 4 is based on Thunderbolt 3 and incorporates Thunderbolt 3. If it's optional, they buried it in the spec? Would love to know where if you do so I can make that clearer. (See https://www.usb.org/usb4 for instance.)
• Apple’s USB 4/Thunderbolt 4 controller ostensibly incorporates all previous standards with backwards compatibility, so the question will likely arise in a specific case: a Thunderbolt 3 device with a Thunderbolt 3 controller attached to a USB 4 controller that isn’t a Thunderbolt 4 controller. In that case, the host computer’s USB 4 controller would have to negotiate down to 10 Gbps and USB 3.1 Gen 2? (???)
• In practice, I wonder which controller modules major brands besides Apple will adopt: it seems most likely they would want USB4/TB4 not USB 4-only?
Per the above about the lawyer, too, the USB-C Charging Cable Apple offers (no video, 480 Mbps USB 2.0 data, and up to 100W power) is absolutely the most maddening cable on the market.
This will need some time to dig into spec to give you the definite answer ( As it was in Spec 1.0 and I dont think they have changed it since ) But if you trust wiki as a reliable source on it [1] under Thunderbolt 3 compatibility
>The USB4 specification states that a design goal is to "Retain compatibility with existing ecosystem of USB and Thunderbolt products." Compatibility with Thunderbolt 3 is required for USB4 hubs; it's optional for USB4 hosts and USB4 peripheral devices.[15] Compatible products need to implement 40 Gbit/s mode, at least 15 W of supplied power, and the different clock; implementers need to sign the license agreement and register a Vendor ID with Intel.[16]
i.e It is part of the USB4 spec, but it is not mandatory.
First thing is that we or at least I haven't found an answer from Intel on the cost of testing and licensing on Thunderbolt. ( So before anyone claiming Intel is greedy, some work has to be done to ensure QA, and work needs money, even if it is just registering an ID. ) Being Royalty free doesn't mean everything else is free. But let's assume it really is free.
Now in my pure logical guess and observation from the current market is that all USB4 host controller right now have at least Thunderbolt 3 compatibility because getting rid of it doesn't save much cost than provider another SKUs. And so far it seems all announced USB4 controller are also TB4 controller for the same reason. As TB4 isn't that much different to TB3.
>In practice, I wonder which controller modules major brands besides Apple will adopt: it seems most likely they would want USB4/TB4 not USB 4-only?
Yes, but that is assuming they cost the same and they dont start doing market differentiation / segmentation. Whether there is an market for cheaper USB4 controller remains to be seen. For example. You could have USB 4 host controller that only support USB4 20 Gbit/s Transport ( not the same as USB 3.2 (20 Gbit/s) ) and not support any Thunderbolt compatibility. Even if that is only a cost saving of possibly pennies I dont think we should underestimate the power of greed. And in fairness if you do millions of unit penny counting is important.
I hope, in pure good faith, that wont happen because it is easier to market existing USB 3 20Gbps and have all USB4 supporting both TB3 and TB4. But again this is not required by spec. And all it takes is a bad actor in the market to do it.
And in all fairness I dont think USB4 Host / or USB - Type C Host were the issue. I do think the consumer should know what the port they buy have support for. But USB-C cable is simply is a bag of hurt.
I found it in the spec in section 2.1.5. (Referring to the May 19, 2021, clean revision of USB4 1.0.)
"A USB4 host or USB4 peripheral device can optionally support interoperability with Thunderbolt 3 (TBT3) products.
"A USB4 hub is required to support interoperability with Thunderbolt 3 products on all of its DFP . A USB4-Based Dock is required to support interoperability with Thunderbolt 3 products on its UFP in addition to all of its DFP.
"When interoperating with a TBT3 product, Thunderbolt Alt Mode is established on the link between products. The USB Type-C Specification describes how a USB4 product negotiates and enters Thunderbolt Alt Mode."
So, accurate!
However, my question is about major brands. Will Lenovo, Dell, etc., go for USB 4-only instead of USB 4/TB 4? I guess we'll find out.
But my understanding would be that a Thunderbolt 4 controller connected by a USB 4 cable to a USB 4-only device running USB 4 for 20 Gbps would still work through Thunderbolt 4’s backwards compatibility across all USB modes.
I'm leaning a bit on three things: • The USB-IF says that USB 4 is based on Thunderbolt 3 and incorporates Thunderbolt 3. If it's optional, they buried it in the spec? Would love to know where if you do so I can make that clearer. (See https://www.usb.org/usb4 for instance.) • Apple’s USB 4/Thunderbolt 4 controller ostensibly incorporates all previous standards with backwards compatibility, so the question will likely arise in a specific case: a Thunderbolt 3 device with a Thunderbolt 3 controller attached to a USB 4 controller that isn’t a Thunderbolt 4 controller. In that case, the host computer’s USB 4 controller would have to negotiate down to 10 Gbps and USB 3.1 Gen 2? (???) • In practice, I wonder which controller modules major brands besides Apple will adopt: it seems most likely they would want USB4/TB4 not USB 4-only?
Per the above about the lawyer, too, the USB-C Charging Cable Apple offers (no video, 480 Mbps USB 2.0 data, and up to 100W power) is absolutely the most maddening cable on the market.