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Primarily it is because USB 4 and Thunderbolt 4 don't implement the same set of functionality. Myopically focusing just on "Gb/s" metrics entirely misses the whole point.
USB 4 only technically optionally covers TB v3 functionality. The USB 4 standards allows TBv3 capability (40Gb/s ) to be omitted from a computer or peripheral with one port ( no upstream and downstream port). And still be labeled "USB 4". You aren't necessarily going to get 40 Gb/s with something labeled "USB 4".
Thunderbolt 4 means pragmatically you have to get 40 Gb/s (with the right cables) from that computer system labeled Thunderbolt. You also are going to get USB 3.1 gen 2 ( and probably also have a 'floor' of USB 3.2 2x2 20 Gb/s USB mode). You are also going to get DisplayPort in almost all cases. Thunderbolt means all the variant stuff that USB 4 says you might get, you do get. You get complete coverage.
( Additionally, it will also probably means that also held to a less minimality's compatibility testing standard too. So the quality is going to be incrementally higher also. Not going to have many "race to the bottom on price" products with the label. )
USB-IF standards typically leave wiggle room for implementers to create stuff that costs less. So a USB Type-C port at the ( 3.1 / 3.2 standard's level absolutely required minimal data connection speed was USB 2.0 . Yes 2.0 ... created in the Year 2000 and port creating in year 2014).
Most likely what Thunderbolt 4 is going to mean is "merged with USB standards " and complete of the laundry list USB "says" it can do.
The current TB v3 controllers don't do USB 3.2 2x2 mode (that maxes out at 20 Gb/s). [they do have a USB "super speed" contorller bolted on though. So it would be an augment. ] So that will probably get added in so they fully support all of the 'slower than 40 Gb/s' USB modes. The USB 4 standard also tries to push the Thunderbolt protocol into a place where there are more than one USB 4 port. ( I think trying to cover USB hub and spoke USB topology instead of the standard 'daisy chain' that Thunderbolt has typically implemented until now. I don't think folks will be happy with that because it will probably raise costs substantially and there will be a huge expectation mismatch between USB 3.0 hub costs and USB 4 hub (really very high speed switch) costs. )
In short, going to more effective use the 40 Gb/s bandwidth that have rather than it being some "drag race" bandwidth bump.
USB-IF has named what most folks commony think of as USB 3.0 three different ways (with very minor differences associated with the ports).
USB 3.0 == USB 3.1 gen 1 == USB 3.2 gen 2 ( all 5 Gb/s of theoretical bandwidth).
This is crowd that Thunderbolt just merged with. Here are the various hierglphs need to know to sort out USB 3.2
Sanity Returns: How USB4's New Logos Will Simplify Shopping
At CES 2020, the USB-IF announced a new USB4 naming scheme that might finally end all the USB confusion!
Thunderbolt? There is just one symbol. One. The above is nine labels. Nine tiny labels that have to fit next to each port with even smaller numbers to read on them.
USB 4 is incrementally better.
USB 4 is a huge improvement because we are now down to six. Thunderbolt 4 still probably has one symbol and no "even more tiny" numbers. So matching the '4' of TB4 to the '4' of USB 4 should be welcome simplicity given the baseline complexity of what USB-IF is doing. The suffix numbers match, so the tech match.
When you make most stuff not optional then don't that to leave a bread trail of indicators of what this particularly implementation left off to shave a couple dollars off the component costs.
That's why. If USB 5 makes all the stuff that Thunderbolt v4 has required mandatory in USB 5 also then perhaps won't need "Thunderbolt" anymore. That is probably not going to happen though. USB-IF is large committee made of folks with a wide variety of interests. A major subgroup is folks who don't want the average selling price of a subset of USB devices to move at all ( and perhaps even get cheaper).
That's taking the 'suffix number match' simplicity too far.
Highly likely not. PCI-e 4.0 has distance traveling issues. A major component of Thunderbolt is about covering relatively longer distances. If try to make Thunderbolt envelope and "swallow" PCI-e v4 will create more issues that Thunderbolt doesn't need right now. Merging with USB is both tactically and strategically more important for next couple of years.
USB 3.2 2x2 largely failed. Passed in 2017 there are very few products that adopt it. It absolutely did not 'kill' Thunderbolt. Adding it to TB controllers would actually probably save it than anything else.
There isn't tons of pressure of user pressure for PCI-e v4 envelopment. If the was overwhemlying broad user bandwidth pressure 3.2 2x2 would have done better. Most users want "more affordable". More effective use of the 40 Gb/s already have.
The major top end bandwidth pusher for Thunderbolt has been covering DisplayPort. (and larger resolutions and increasing color bit levels at larger resolutions). DisplayPort 2.0 basically adopted the foundation to Thunderbolt (the baseline protocols). it 'solved' the 'next step' problem by turning all the communication unidirectional. So instead of 40 Gb/s both to and from it is just 80 Gb/s to the display.
Bidirectional > 40Gb/s there just aren't very many broad based use cases. Yes can find corner cases but how many folks want that right now? And is that worth "blowing up" the merger with USB ( because Intel is moving the TB target as 3rd party implementors are trying to get their TBv3 implementations working).
P.S. Thunderbolt 4 could do some work too on the encoded PCI-e data flow management.
The USB approach of sub-setting the data lanes to fixed types ( allocated on plug-in event, but fixed after the plug-in is settled ) doesn't work as well has scale up. You end up with allocations of wasted bandwidth. Thunderbolt v3 implementations are good but they could be better.
The iMac Pro and the 2019 Macs both technically have TBv3 controllers in them. The "alpine ridge" controller in the iMac Pro can only go up to DisplayPort v1.2 data transmission. The "Titan Ridge" can cover DisplayPort 1.4 ( and DSC compressed ) streams. So that leads to differences in support for the XDR. For example a list of bandwidths from the XDR buyers thread. So Intel iterated on DisplayPort.
Intel could do something similar to the PCI-e v3 traffic where could work on the flow control hueristics and let the PCI-e flow at higher rates when there is almost zero DisplayPort traffic on the network. More efficient use and sharing of multiple protocols over the same set of wires is why Thunderbolt got added to USB. Using 40 Gb/s more effectively would be an improvement. Typically Intel hasn't bumped the TB major version number just for such improvements. But lifting the USB naming fog would be a convienent time to make that shift with that "smaller" change.
The implementation of multiple port switch from "cost effective daisy chain" would be a major move and not be a "bandwidth bump" at all.
I still dont see the point. It just making us so confused about USB and TB standards again and again.
And base on the official article from Intel, they didnt mention anything about the version of USB 3. Just USB 3.
Primarily it is because USB 4 and Thunderbolt 4 don't implement the same set of functionality. Myopically focusing just on "Gb/s" metrics entirely misses the whole point.
USB 4 only technically optionally covers TB v3 functionality. The USB 4 standards allows TBv3 capability (40Gb/s ) to be omitted from a computer or peripheral with one port ( no upstream and downstream port). And still be labeled "USB 4". You aren't necessarily going to get 40 Gb/s with something labeled "USB 4".
Thunderbolt 4 means pragmatically you have to get 40 Gb/s (with the right cables) from that computer system labeled Thunderbolt. You also are going to get USB 3.1 gen 2 ( and probably also have a 'floor' of USB 3.2 2x2 20 Gb/s USB mode). You are also going to get DisplayPort in almost all cases. Thunderbolt means all the variant stuff that USB 4 says you might get, you do get. You get complete coverage.
( Additionally, it will also probably means that also held to a less minimality's compatibility testing standard too. So the quality is going to be incrementally higher also. Not going to have many "race to the bottom on price" products with the label. )
USB-IF standards typically leave wiggle room for implementers to create stuff that costs less. So a USB Type-C port at the ( 3.1 / 3.2 standard's level absolutely required minimal data connection speed was USB 2.0 . Yes 2.0 ... created in the Year 2000 and port creating in year 2014).
Most likely what Thunderbolt 4 is going to mean is "merged with USB standards " and complete of the laundry list USB "says" it can do.
The current TB v3 controllers don't do USB 3.2 2x2 mode (that maxes out at 20 Gb/s). [they do have a USB "super speed" contorller bolted on though. So it would be an augment. ] So that will probably get added in so they fully support all of the 'slower than 40 Gb/s' USB modes. The USB 4 standard also tries to push the Thunderbolt protocol into a place where there are more than one USB 4 port. ( I think trying to cover USB hub and spoke USB topology instead of the standard 'daisy chain' that Thunderbolt has typically implemented until now. I don't think folks will be happy with that because it will probably raise costs substantially and there will be a huge expectation mismatch between USB 3.0 hub costs and USB 4 hub (really very high speed switch) costs. )
In short, going to more effective use the 40 Gb/s bandwidth that have rather than it being some "drag race" bandwidth bump.
USB-IF has named what most folks commony think of as USB 3.0 three different ways (with very minor differences associated with the ports).
USB 3.0 == USB 3.1 gen 1 == USB 3.2 gen 2 ( all 5 Gb/s of theoretical bandwidth).
This is crowd that Thunderbolt just merged with. Here are the various hierglphs need to know to sort out USB 3.2
Sanity Returns: How USB4's New Logos Will Simplify Shopping
At CES 2020, the USB-IF announced a new USB4 naming scheme that might finally end all the USB confusion!
Thunderbolt? There is just one symbol. One. The above is nine labels. Nine tiny labels that have to fit next to each port with even smaller numbers to read on them.
USB 4 is incrementally better.
USB 4 is a huge improvement because we are now down to six. Thunderbolt 4 still probably has one symbol and no "even more tiny" numbers. So matching the '4' of TB4 to the '4' of USB 4 should be welcome simplicity given the baseline complexity of what USB-IF is doing. The suffix numbers match, so the tech match.
When you make most stuff not optional then don't that to leave a bread trail of indicators of what this particularly implementation left off to shave a couple dollars off the component costs.
That's why. If USB 5 makes all the stuff that Thunderbolt v4 has required mandatory in USB 5 also then perhaps won't need "Thunderbolt" anymore. That is probably not going to happen though. USB-IF is large committee made of folks with a wide variety of interests. A major subgroup is folks who don't want the average selling price of a subset of USB devices to move at all ( and perhaps even get cheaper).
That's taking the 'suffix number match' simplicity too far.
Highly likely not. PCI-e 4.0 has distance traveling issues. A major component of Thunderbolt is about covering relatively longer distances. If try to make Thunderbolt envelope and "swallow" PCI-e v4 will create more issues that Thunderbolt doesn't need right now. Merging with USB is both tactically and strategically more important for next couple of years.
USB 3.2 2x2 largely failed. Passed in 2017 there are very few products that adopt it. It absolutely did not 'kill' Thunderbolt. Adding it to TB controllers would actually probably save it than anything else.
There isn't tons of pressure of user pressure for PCI-e v4 envelopment. If the was overwhemlying broad user bandwidth pressure 3.2 2x2 would have done better. Most users want "more affordable". More effective use of the 40 Gb/s already have.
The major top end bandwidth pusher for Thunderbolt has been covering DisplayPort. (and larger resolutions and increasing color bit levels at larger resolutions). DisplayPort 2.0 basically adopted the foundation to Thunderbolt (the baseline protocols). it 'solved' the 'next step' problem by turning all the communication unidirectional. So instead of 40 Gb/s both to and from it is just 80 Gb/s to the display.
Bidirectional > 40Gb/s there just aren't very many broad based use cases. Yes can find corner cases but how many folks want that right now? And is that worth "blowing up" the merger with USB ( because Intel is moving the TB target as 3rd party implementors are trying to get their TBv3 implementations working).
P.S. Thunderbolt 4 could do some work too on the encoded PCI-e data flow management.
The USB approach of sub-setting the data lanes to fixed types ( allocated on plug-in event, but fixed after the plug-in is settled ) doesn't work as well has scale up. You end up with allocations of wasted bandwidth. Thunderbolt v3 implementations are good but they could be better.
The iMac Pro and the 2019 Macs both technically have TBv3 controllers in them. The "alpine ridge" controller in the iMac Pro can only go up to DisplayPort v1.2 data transmission. The "Titan Ridge" can cover DisplayPort 1.4 ( and DSC compressed ) streams. So that leads to differences in support for the XDR. For example a list of bandwidths from the XDR buyers thread. So Intel iterated on DisplayPort.
Intel could do something similar to the PCI-e v3 traffic where could work on the flow control hueristics and let the PCI-e flow at higher rates when there is almost zero DisplayPort traffic on the network. More efficient use and sharing of multiple protocols over the same set of wires is why Thunderbolt got added to USB. Using 40 Gb/s more effectively would be an improvement. Typically Intel hasn't bumped the TB major version number just for such improvements. But lifting the USB naming fog would be a convienent time to make that shift with that "smaller" change.
The implementation of multiple port switch from "cost effective daisy chain" would be a major move and not be a "bandwidth bump" at all.
This is crowd that Thunderbolt just merged with. Here are the various hierglphs need to know to sort out USB 3.2
Thunderbolt? There is just one symbol. One. The above is nine labels. Nine tiny labels that have to fit next to each port with even smaller numbers to read on them.
