Intel teased the Thunderbolt 4 interface earlier this year at CES 2020 with little detail, though a bit of digging revealed that the new interface isn't faster than the existing Thunderbolt 3. With speeds up to 40Gb/s, Thunderbolt 4 maintains the same maximum speed rating as its predecessor and doesn't enable new features.
However, the new specification requires vendors to enable all of the optional features built into Thunderbolt 3, like the ability to hit the 40Gb/s data throughput requirements and support two 4K displays or one 8K display, in order to qualify for Thunderbolt 4 certification. The specification will debut with Intel's Tiger Lake processors.
The specification also requires support for PC charging on at least one computer port (for devices under 100W) and support for Intel's existing VT-d based DMA protection, which plugs a security hole in the Thunderbolt interface that allowed devices to access system memory. This feature is required with the specification, which doesn't make it clear whether or not AMD-powered systems can achieve Thunderbolt 4 certification. Intel responded that the spec is available to AMD, but hasn't clarified how AMD could bring its systems into compliance without support for VT-d, or if such an arrangement can be enabled. [EDIT: Intel reached out to clarify that AMD, and other vendors, can use Thunderbolt 4 with equivalent DMA protection technology] This could be a sticking point, as AMD systems with even Thunderbolt 3 certification are still a rarity.
Intel also announced new 8000-series controllers that will bring support for four ports on Thunderbolt 4 (TB4) docks. The new silicon will power a new wave of Thunderbolt docks that feature one upstream connection to the PC and three downstream connections to attached peripherals, like storage devices and monitors.
Intel contributed the Thunderbolt 4 specification to the USB standards committee last year to further adoption of the Thunderbolt interface, and the unficiation of the two standards, along with forced compliance with all of the features of Thunderbolt 3 and USB4, is designed to simplify the confusion surrounding the cornucopia of different ports and cables used for both USB and Thunderbolt interfaces. In the end, that could help the industry unify the current fragmented cable and port compatibility into one type of USB-C type cable for both the USB and Thunderbolt interfaces.
The table above shows the minimum level of support that vendors, like PC makers, have to enable to gain the Thunderbolt certification badge. All of the features we see enabled on the Thunderbolt 4 column already exist in the Thunderbolt 3 specification, but many of those features, like the ability to hit the maximum rated 32Gb/s of throughput, support for PC charging, and USB4 compliance, were previously optional.
Thunderbolt 4 also calls for universal cables (up to 2 meters in length) that support 40Gb/s of throughput, addressing the current confusing array of different types of USB-C cables and ports into one central solution that has a simplified branding scheme (a single lighting bolt logo). Thunderbolt 4 cabling will come in 0.2m, 0.8m, and 2m lengths, with plans for 5 to 50m cabling in the future.
Intel's 'Maple Ridge' 8000-series Thunderbolt 4 controllers includes JHL8540 and JHL8340 host controllers for PC vendors, which will allow integration with systems powered by other types of processors, and the JHL8440 device controller for accessories. Intel says it has made developer kits and certification testing available for vendors. The first Thunderbolt 4 systems will arrive later this year, including with Athena 2.0 laptops, and accessories will also become available.
Manufacturers of end devices pay a one-time fee for Thunderbolt 4 certification and relevant trademark licensing, which are the only payments required to obtain the Thunderbolt 4 badge, but cable makers are subject to ongoing rigorous inspections that include spot checks and factory audits to ensure that quality remains acceptable on an ongoing basis. Intel also hosts plugfests, during which interoperability with numerous new devices is tested, and workshops.