Question The extent of Thunderbolt 4's support for USB4

[KeyserTomassi]

USB4 comes in 2 different speeds: USB4 20 Gbps & USB4 40 Gbps.

When Intel says Tiger Lake's Thunderbolt 4 includes USB4, does this necessarily mean that all Thunderbolt 4 ports include support for USB4 40 Gbps? Or can the manufacturer choose to only support USB4 20 Gbps?

In other words, is it possible to come across a Thunderbolt 4 port that, while supporting Thunderbolt 4 devices at 40 Gbps, only supports USB4 devices at a maximum of 20 Gbps? Or is that not an option under the Thunderbolt 4 certification?

 

[siaan312]

I don't understand the question fully so i'll just explain this:

Thunderbolt 4 is very similar to thunderbolt 3, with these changes: hardware mitigations for vulnerabilities, and a more strict standard that will always support 4x pcie instead of 2 and some other small stuff you don't have to worry about.
It is 40gigabit.

USB 4 is the "open source" standard for thunderbolt 3.
It is interchangeable with thunderbolt 3 and 4 almost across the board, and is so similar they can, and a lot of times use the same drivers.
But USB 4, since it is less strict, and, well, open source, it has less strict rules and can support more, or less feature's depending on the one integrating it.

There is no USB 4 20 gig. That is usb 3.2 gen 2x2.

 

[KeyserTomassi]

@siaan312 Thank you for responding. I understand the differences between Thunderbolt 3 & Thunderbolt 4. I also understand what USB4 is and how it relates to both TB3 & TB4.

I also understand that a USB4 40 Gbps port does not necessarily support Thunderbolt 4, but a Thunderbolt 4 port does indeed support USB4.

There is no USB 4 20 gig. That is usb 3.2 gen 2x2.

I'm afraid this is incorrect.

Yes, USB 3.2 Gen 2x2 operates at 20 Gbps, but USB4 20 Gbps actually exists. It is meant for devices, possibly lower-end laptops and smartphones, that want to implement USB4 without needing the full 40 Gbps speed. In other words, 40 Gbps in USB4 is actually optional. That's where my questions comes from:

Does Thunderbolt 4 necessarily support USB4 at the full speed of 40 Gbps, or can some Thunderbolt 4 ports support only USB4 20 Gbps?

Feel free to read more about the USB4 20 Gbps variant here:
https://en.wikipedia.org/wiki/USB4

And here is a link to the official USB4 Specification Language Usage from the USB-IF, which clearly discusses USB4 20 Gbps:
https://www.usb.org/sites/default/files/usb4_language_product_and_packaging_guidelines_final__0.pdf

Also, here are two screenshot I took from the Thunderbolt 4 official announcement press deck. You will clearly see USB4 20. Here is a link to the entire deck:
https://newsroom.intel.com/wp-conte...ntel-thunderbolt4-announcement-press-deck.pdf

It does not explicitly specify whether USB4 40 Gbps is an integral part of Thunderbolt 4. Again, just because Thunderbolt 4 itself operates at 40 Gbps does not necessarily mean that devices that only support USB4 40 Gbps will operate at 40 Gbps. This is the point I need to clarify.

 

[siaan312]

@siaan312 Thank you for responding. I understand the differences between Thunderbolt 3 & Thunderbolt 4. I also understand what USB4 is and how it relates to both TB3 & TB4.

I also understand that a USB4 40 Gbps port does not necessarily support Thunderbolt 4, but a Thunderbolt 4 port does indeed support USB4.



I'm afraid this is incorrect.

Yes, USB 3.2 Gen 2x2 operates at 20 Gbps, but USB4 20 Gbps actually exists. It is meant for devices, possibly lower-end laptops and smartphones, that want to implement USB4 without needing the full 40 Gbps speed. In other words, 40 Gbps in USB4 is actually optional. That's where my questions comes from:

Does Thunderbolt 4 necessarily support USB4 at the full speed of 40 Gbps, or can some Thunderbolt 4 ports support only USB4 20 Gbps?

Feel free to read more about the USB4 20 Gbps variant here:
https://en.wikipedia.org/wiki/USB4

And here is a link to the official USB4 Specification Language Usage from the USB-IF, which clearly discusses USB4 20 Gbps:
https://www.usb.org/sites/default/files/usb4_language_product_and_packaging_guidelines_final__0.pdf

Also, here are two screenshot I took from the Thunderbolt 4 official announcement press deck. You will clearly see USB4 20. Here is a link to the entire deck:
https://newsroom.intel.com/wp-conte...ntel-thunderbolt4-announcement-press-deck.pdf

It does not explicitly specify whether USB4 40 Gbps is an integral part of Thunderbolt 4. Again, just because Thunderbolt 4 itself operates at 40 Gbps does not necessarily mean that devices that only support USB4 40 Gbps will operate at 40 Gbps. This is the point I need to clarify.

got it, guess you learn something everyday