Intel earlier this week updated its desktop processor product stack with the introduction of the 14th Gen Core "Raptor Lake Refresh" processors. During our coverage of the processor, we erroneously mentioned that the processor supports the upcoming Thunderbolt 5 connectivity standard. Intel reached out to us for a correction, which revealed an interesting detail. Apparently, 14th Gen Core desktop processors do not support Thunderbolt 5, even though Intel has their own TB5 controller design codenamed "Barlow Ridge". However, these won't arrive before Q1 2024, the currently shipping "Maple Ridge" controller has only support for Thunderbolt 4. But even once Barlow Ridge is available, they will not be compatible with "Raptor Lake Refresh" socketed desktop processors.

Intel announced the Thunderbolt 5 standard in September, around the same time, it provided a technical reveal of its upcoming Core "Meteor Lake" mobile processors. The new standard provides a generational doubling in bandwidth to 80 Gbps (per direction), but relies on an exotic new feature called Bandwidth Boost. With this feature enabled, users get 120 Gbps of bandwidth in a particular direction, and 40 Gbps on its opposite direction.Bandwidth Boost should come in handy when, for example, you are importing a large data set from a Thunderbolt 5-based external storage device to your local machine. In such a case, the receiving (Rx or inbound) bandwidth is boosted to 120 Gbps, while reducing the transmission (Tx or outbound) bandwidth to 40 Gbps. When exporting a large amount of data to this external Thunderbolt 5 storage device, the roles are reversed, where the Tx bandwidth is boosted at the expense of the Rx bandwidth.

It's important to take a moment to understand how Intel arrives at 80 Gbps as the default per-direction bandwidth of Thunderbolt 5, even when the underlying PCIe bandwidth of PCIe Gen 4 x4 adds up to 64 Gbps per direction—Thunderbolt is a complex bus, which combines a number of links besides PCIe, such as DisplayPort, which is how it arrives at its advertised bandwidth. So 80 Gbps is really just 64 Gbps of underlying PCIe bandwidth, and 120 Gbps is really just 96 Gbps, and the current Thunderbolt 4 that boasts of 40 Gbps/direction is really just 32 Gbps/direction PCIe.

Thunderbolt and USB4 are PCIe-based serial interconnect standards. Each PCIe lane has physical wiring for Rx and Tx. The way we understand Thunderbolt 5 Bandwidth Boost to work, for the ability to push 120 Gbps through a PCI-Express 4.0 x4 connection between the "Barlow Ridge" controller and the processor's PCIe root complex, the root complex should be able to re-task both sub-lanes of two of the four PCIe lanes for either purely-Tx or purely-Rx. This probably requires some awareness at the end of the PCIe root complex that's part of the processor's uncore.In the Intel slide above, the company details how Bandwidth Boost works at the Thunderbolt 5 link layer. Two 40 Gbps links per direction normally make up the 80 Gbps per-direction bandwidth of Thunderbolt 5. With Bandwidth Boost enabled, three out of four links are loaded toward one direction to make 120 Gbps, while the last link is in the opposite direction. As for which direction gets the Bandwidth Boost depends entirely on the application, as detailed in the examples above. You get get a 120 Gbps high-speed transmit with a 40 Gbps receive, or a 120 Gbps high-speed receive with a 40 Gbps transmit. The second image drawn by us, illustrates how the PCIe backend works between the Thunderbolt 5 host controller and the PCIe root complex.

Without this uncore-level awareness, for Thunderbolt 5 to be able to push 120 Gbps to a downstream device, there needs to be a PCIe Gen 4 x8 connection between the PCIe root and the "Barlow Ridge" host controller that can provide 160 Gbps of per-direction bandwidth, which is both undesirable and unlikely, as all prior generation discrete Thunderbolt controllers by Intel have used a PCIe x4 connection to the platform.

Intel also stated that when "Barlow Ridge" does come out in Q1 2024, it will have compatible processors at launch, without stating what those processors are. It's possible that Intel is updating its mobile processor stack, and those processors will support Thunderbolt 5 the way Intel intends it (including the Bandwidth Boost feature). Intel already provided a technical deep-dive of its upcoming Core "Meteor Lake" mobile processor, without mentioning product launch dates. The 2024 International CES (January) provides Intel with the perfect opportunity to launch new processors. Intel put out this statement as an October 19 editor's note in its newsroom article announcing the 14th Gen Core desktop processors:

While some processors in the Intel Core 14th Gen processor family will include support for Thunderbolt 5, Intel Core 14th Gen desktop processors, specifically, will not support it. The Intel Core 14th Gen launch announcement incorrectly said, "Intel Core 14th Gen desktop processors include support for … upcoming Thunderbolt 5 wired connectivity - supporting up to 80 Gbps of bi-directional bandwidth." Intel will share additional details on Intel Core 14th Gen CPUs that support Thunderbolt 5 at a later date.

The above Intel statement says that some 14th Gen processors will support Thunderbolt 5, but not the 14th Gen Core desktop processors. Intel's "Meteor Lake" mobile processor does not come with 14th Gen Core branding, but debuts a new brand nomenclature, which leaves us with only one possibility, non-socketed 14th Gen Core processors, namely "Raptor Lake Refresh" mobile (-H and -HX). With "Meteor Lake" on the horizon, Intel may push "Raptor Lake Refresh" to the -H and -HX segments much in the same way as those segments in the 10th Gen were addressed by "Comet Lake," as "Ice Lake" handled the -U and -P segments. It's very likely that these "Raptor Lake Refresh-H/HX" processors are the ones that support Thunderbolt 5 from the 14th Gen using "Barlow Ridge" controllers, besides the upcoming "Meteor Lake" processors that have "Thunderbolt 5" integrated as part of its SoC tile.

Users on the 14th Gen Core socketed desktop platform can enjoy Thunderbolt 4 using motherboards or add-on cards that have Intel's "Maple Ridge" controller that's been in the market since 2020, which provides 40 Gbps per direction bandwidth. Thunderbolt 5 and AI Boost are two features that will only make it to socketed desktop platforms with Intel's next-generation processors. We know that "Meteor Lake" is confirmed not coming to socketed desktop platforms, which leaves us with "Arrow Lake-S," bound for the second half of 2024.