Thunderbolt 4 is pretty likely to be just Thunderbolt 3 with some tweaks to keep it in compliance with USB 4 . They'll also match on numbers TB 4 goes with USB 4 which will minimize consumer confusion.
Folks are saying it is faster and different on some flimsy evidence. Intel said it was 4x faster than USB. But they didn't say which USB. USB 3.0 ( or USB 3.1 gen 1 or whatever name want to use) is 10Gb/s. 4x that is 40 Gb/s. TBv3 is 40 Gb/s. Done 4x !
The hand waving occurs when folks run off and try to pick up the USB 3.2 which pragmatically nobody uses and then try to slap a 4x on 20Gb/s. That would lead to a new 80Gb/s. That is really suspect. If it was really big bragging Intel was doing they'd probably would have said USB 3.2. They didn't.
There may be a 80Gb/s mode in Thunderbolt 4 but that would to support DisplayPort 2.0. But that 80 only comes from making the whole network unidirectional going outbound. It using the base Thunderbolt protocol but isn't the primary Thunderbolt mode. It would though be consistent in Thunderbolt controllers supporting a "alternative DisplayPort" only mode that they have had from the start. If there is any 80Gb/s that's probably what it is ( i.e., support for direct connect 8K displays or super high refresh displays).
The other speculative push is that Thunderbolt 4 is going to push PCI-e v4. I doubt that. First, it would be disruptive with this whole "merge" with USB that is going on now. Same with the usage by DisplayPort. Second the cables would get even more expensive ... which again is the wrong timing to do that. Third the integrated TB controllers design that Intel did with Ice Lake had x4 PCI-e v3 done to each sub controllers.
www.anandtech.com
Each port can be x4 driven by a controller. That is collectively x16 PCI-e v3 worth of bandwidth right there. Optimize that. before jumping to PCI-e v4. ( or could use x8 of PCI-e internally inside the CPU complex to be easier to route and then downshift and ship out over the TB switch/router. ).
What Intel is likely doing in Tiger Lake is an straightforward iteration on what they did with Ice Lake.
Finally, it doesn't make any sense at all to ramp the CPU's controllers up to nose bleed levels if there are no discrete controllers that can also go at that speed. So far there are zero controllers built by someone other than Intel. Let the 3rd parties correctly implement the TBv3 speeds and merge with USB 4. Once there are multiple players only then can pragmatically move Thunderbolt forward (primarily under USB-IF control ..... which is likely going to be measured and relatively slow. )
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Which uses an Intel TB controller. There are still no 2nd party TB controllers. That is exactly why it is grossly the wrong time for Thunderbolt to suddenly move out from under anyone who is working on a USB4 (merged with TBv3 ) one.
Frankly, all this integrated with the CPU stuff doesn't have much real impact until there are discrete controllers for the peripherals. Until that market is flushed out TBv4 in the CPU would be a "bridge to nowhere" if radically different than what is supported by USB 4.
If TB4 is just USB 4 with the somewhat optional TBv3 elements always turned on then it probably won't be Intel only. Technically the USB 4 standard has some wiggle room to not implement TBv3 in certain contexts. It is still going to be have to have some of the "optional" stuff present to have the TB functionality. It is pretty likely that stuff being unambiguously present is what Intel is calling TB4.
There is no deep need for PCI-e v4 to be looped in here. What should be a much higher priority is to complete the merge with USB4 and get broader adoption. Then maybe PCI-e v4 can be looped in later, but 40Gb/s ( if get to close to the full allocation for PCI-e v3 traffic on the wire when DisplayPort not active. ) would be highly useful. Especially with broader adoption (and hopefully economies of scale lower entry prices).
The way Intel is doing it with the mainstream chips, the PCI-e lanes are only internally allocated so don't really have to loose any external links. Ice Lake has more connectivity than any previous TB controllers PCI-e lane wise.