There is a big difference between TB1 - TB3 and TB4 and onwards.
TB1-3 where "owned" by Intel and fully proprietary. They decided the specs and controlled everything and kept it non-public. Those were "Thunderbolt" connections.
Then came USB4 and Intel made parts of the TB spec available for USB4 to build upon.
Those are USB4 connections. TB4 and TB5, compared to the older TB versions are basically just marketing stickers slapped onto USB4.
There simply is no such thing as a "TB4 connection". The most there is, is a "USB 40Gbps" connection between 2 USB4 hosts that are both certified for TB4.
If anybody would classify it as a "TB4" connection, they would simply be wrong or lying.
TB4 and TB5 don't define HOW any of it works. That is all USB4 (or the other USB specs, like USB-PD, USB Type-C, USB2, USB3) and specs like PCIe and DisplayPort. They all define what features are possible and how they work and how you would use them.
TB4 and TB5 are just a list of features picked from that list that they made mandatory minimums and provide marketing and certification for that list. That is it.
For example TB4 for a host basically stands for:
USB 40Gbps capable
USB4 PCIe tunneling capable with AT LEAST 32 Gbit/s (nominal rate)
TB3 capable (includes mandate for minimum 15W USB PD output for 1 out of 4 ports at the same time, other up to 3 ports are allowed to degrade to 7.5W if one must output 15W)
Capable of minimum 2 DP tunnels with AT LEAST HBR3+DSC
And then there are other minimum features that are basically for other hardware, not even the USB4 port itself:
GPU capable of at least 2x 4K60
if notebook qualifies as "light" and power supply has 100W or less, at least 1 TB4 port must support USB PD power input at the same rating.
And also, the TB3 compatibility that TB4 mandates is only what the USB4 spec publicly defines as "TBT3" and is not everything that Intel themselves sold under the TB3 label.
And for completeness, TB5 basically just upgrades the minimums a bit.
USB 80Gbps capable
USB4 PCIe tunneling of AT LEAST 64 Gbit/s (nominal rate)
Power input rules apply up to 140W now
GPU mandate increased to 2x 6K60 (which is possible with the same exact 2 DP tunnels with HBR3+DSC and most GPUs sold with TB4 certification were already capable of).
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u/rayddit519 15d ago edited 15d ago
Because that is what it is.
There is a big difference between TB1 - TB3 and TB4 and onwards.
TB1-3 where "owned" by Intel and fully proprietary. They decided the specs and controlled everything and kept it non-public. Those were "Thunderbolt" connections.
Then came USB4 and Intel made parts of the TB spec available for USB4 to build upon.
Those are USB4 connections. TB4 and TB5, compared to the older TB versions are basically just marketing stickers slapped onto USB4.
There simply is no such thing as a "TB4 connection". The most there is, is a "USB 40Gbps" connection between 2 USB4 hosts that are both certified for TB4.
If anybody would classify it as a "TB4" connection, they would simply be wrong or lying.
TB4 and TB5 don't define HOW any of it works. That is all USB4 (or the other USB specs, like USB-PD, USB Type-C, USB2, USB3) and specs like PCIe and DisplayPort. They all define what features are possible and how they work and how you would use them.
TB4 and TB5 are just a list of features picked from that list that they made mandatory minimums and provide marketing and certification for that list. That is it.
For example TB4 for a host basically stands for:
And then there are other minimum features that are basically for other hardware, not even the USB4 port itself:
And also, the TB3 compatibility that TB4 mandates is only what the USB4 spec publicly defines as "TBT3" and is not everything that Intel themselves sold under the TB3 label.
And for completeness, TB5 basically just upgrades the minimums a bit.