For anyone who has used a Mac laptop in recent years, or a top-end Windows notebook, Thunderbolt 3 has probably been on their radar—and perhaps had them scratching their heads regarding what it can do. This port looks like one of the new-style, oval USB Type-C connectors, but it does a bunch more: It can carry a video signal using the DisplayPort protocol, charge connected devices, and allow for data transfers at speeds beyond what simple USB can manage. (See our explainer, Thunderbolt 3 vs. USB-C: What’s the Difference?)
The story of the latest flavor of the Thunderbolt interface—Thunderbolt 4—starts with a change in direction, however. Intel opened up the Thunderbolt 3 protocol to USB’s controlling consortium (the USB-IF) for royalty-free use in the development of next-generation USB4, delivering faster speeds and interoperability to USB4 devices. Indeed, the fates and directions of the two new “4” specs are intertwined. (And yes, the USB team dropped the space in “USB4.” That’s not a typo.)
This move toward open source didn’t mean, however, that Intel stopped developing its traditionally proprietary Thunderbolt specification. Intel has kept moving Thunderbolt down the tracks and announced Thunderbolt 4 a year ago at CES 2020, and new Thunderbolt 4-equipped PCs based on Intel’s 11th Generation (“Tiger Lake”) Core processors are just now starting to roll out. These Tiger Lake-based computers are also ushering in USB4 connectivity, so there is bound to be some confusion with Thunderbolt 4 and USB4 both arriving at the same time…and sometimes, on the same actual ports.
Also muddling up the picture is Thunderbolt 4’s lack of a single headline-grabbing feature—such as a faster top-end speed than its predecessor. Thunderbolt 4 isn’t a speed play; it is more about minimum requirements than maximum speeds. To help you sort out how Thunderbolt 4 differs from Thunderbolt 3, as well as from USB4, we’ve prepared a little primer on the state of play.
Thunderbolt: A Bit of History
Before we get into the specifics of the new Thunderbolt 4 protocol, let’s first back up and explain what Thunderbolt is and does, and how we got here.
Introduced by Intel and Apple, Thunderbolt first showed up on a MacBook Pro in 2011. The physical form of the port was a mini DisplayPort connector with a little lightning-strike icon next to it. It combined DisplayPort and PCI Express technologies in a single cable to drive high-resolution displays and high-speed data transfers with a top speed of 10Gbps. Using the same physical port, Thunderbolt 2 doubled the bandwidth to 20Gbps and added DisplayPort 1.2 support, giving the interface the ability to drive a video signal to a 4K display.
Thunderbolt 3 doubled the data rate—again—to 40Gbps. Another big change: Thunderbolt 3 no longer used the mini DisplayPort connector as its physical interface, dropping it in favor of the USB Type-C port, with the technology piggybacking on that connector, in the same way that Thunderbolt 1 and 2 piggybacked on mini DisplayPort. It also added up to 100 watts of power via USB Power Delivery (USB PD), so you could use your PC to charge your phone and other USB devices—or even charge a laptop over the port. The Thunderbolt 3 spec also introduced Thunderbolt networking with 10Gbps Ethernet. Thunderbolt 3 provided enough video bandwidth that it led to a wide array of applications, from single-cable docks that could also charge your devices, to external GPUs to supercharge a laptop’s graphics capabilities.
Thunderbolt 4 vs. Thunderbolt 3: What’s the Difference?
Thunderbolt 4 doesn’t offer any headline-grabbing improvements over Thunderbolt 3. On the surface, the two protocols appear very similar. Both use the USB Type-C physical connector. Both offer a maximum throughput of 40Gbps. Both offer at least 15 watts and up to 100 watts of charging power. And both offer support for that 10Gbps networking.
Underneath the surface, however, Thunderbolt 4 has a number of significant advantages. For starters, it doubles the minimum video and data requirements of Thunderbolt 3. Thunderbolt 4 will support sending a video signal to two 4K displays, or to one 8K display, where Thunderbolt 3 is required to support only a single 4K display. And where Thunderbolt 3 systems have to support only a 16Gbps data rate via PCI Express, Thunderbolt 4 will double that requirement to 32Gbps. That added bandwidth will certainly be put to good use by anyone who regularly transfers gigantic files of high-resolution video and other large data sets from storage drives to their PC for editing.
Thunderbolt 4 will also lead to more capable peripherals. You’ll see Thunderbolt 4 docks and monitors with four Thunderbolt 4 ports, double the two ports, at most, you’ll find on Thunderbolt 3 devices. New thin-and-light laptops that need less than 100 watts to charge will be required to offer USB Type-C charging on at least one of their Thunderbolt 4 ports. And when a Thunderbolt 4 laptop is connected to a Thunderbolt 4 dock, it must be able to wake from sleep from a connected keyboard or mouse. Thunderbolt 4 cables will also support 40Gbps throughput at up to two meters in length, up from the 0.5-meter maximum of a passive Thunderbolt 3 cable.
With the ability to daisy-chain up to six Thunderbolt devices, you have the ability to connect multiple devices without each one needing a direct connection to your computer. Combined with Thunderbolt 4’s greater charging and wake-from-sleep capabilities and longer cables, you’ll have more flexibility in setting up your workspace to make your office less cluttered with wires and your office life a bit easier.
Thunderbolt 4 vs. USB4: The Key Differences
Now, in practical fact, it’s easy to confuse Thunderbolt 4 and USB4. They both use the USB Type-C connector. They both offer a maximum bandwidth of 40Gbps. They are both getting introduced with Intel’s new 11th Generation “Tiger Lake” Core processors. And Thunderbolt 4 supports USB4, meaning you can connect a USB device to your laptop’s Thunderbolt port. Thunderbolt 4 is also backward compatible with Thunderbolt 3. In both instances, however, the connection will default to the slower speeds of USB4 or Thunderbolt 3.
Thunderbolt 4 is basically a guarantee that you are getting the best version of USB4. While USB4 offers the same 40Gbps speed as Thunderbolt 4, there is also a slower 20Gbps version of USB4. Thunderbolt 4 also guarantees you can run a pair of 4K displays at minimum and transfer data at up to 32Gbps. With USB4, you are guaranteed only the minimums of running a single display and a 16Gbps data rate. A USB4 hub also lacks the mandatory charging and wake-from-sleep requirements of Thunderbolt 4, as well as 10Gbps networking.
USB4 does have one advantage over Thunderbolt 4: logos that are more informative. With USB4, you should see “USB 20Gbps” and “USB 40Gbps” logos next to USB Type-C ports that will tell which flavor of USB4 you are dealing with. Unfortunately, Intel does not offer such specifics with its Thunderbolt logos. A Thunderbolt logo is a Thunderbolt logo is a lightning bolt, with no way to tell just by glancing at the side of your laptop or your desktop PC’s I/O panel whether a port is version 1, 2, 3, or 4 of Thunderbolt. (The connector will tell you if it is Thunderbolt 1 or 2 versus Thunderbolt 3 or 4, but that’s all you can assume on sight.) You’ll need to consult your user manual or spec sheet to know which version of Thunderbolt a device offers. (Some Thunderbolt 4 cables might include a “4” next to the Thunderbolt 4 logo, but such specificity is not usually offered on laptops.)
Security Against Thunderspy
One last advantage that Thunderbolt 4 offers over Thunderbolt 3 is better security against Thunderspy attacks. In such a potential attack, a hacker can steal your data via vulnerabilities of a Thunderbolt port. Such an attack requires physical access to your device, but it takes all of five minutes and is effective even when your laptop is locked or sleeping, or your hard drive is encrypted.
A Thunderspy attack is able to work by taking advantage of the PCI Express portion of Thunderbolt and its direct memory access (DMA), which bypasses the CPU to enable fast access to system memory. Thunderbolt 4 requires Intel’s Virtualization Technology for Directed I/O (VT-d), which protects against DMA attacks.
How this works: VT-d offers DMA remapping, which isolates a portion of system memory for a connected device, so that the device cannot read or write to other areas of your memory. It basically walls off a portion of system memory for a Thunderbolt device, so it can’t access other places in the memory to overwrite, say, your device’s password protection.
To be sure, this vulnerability is a very remote threat for most folks. It’s mainly a concern for corporate laptops that may travel a lot, get left in unsecured locations, and contain extremely sensitive financial or other business data.
Thunderbolt 4’s Arrival: Rolling Thunder
Thunderbolt 4 laptops based on Intel’s 11th Generation “Tiger Lake” Core processors are only now starting to roll out. We saw the first Tiger Lake laptops with Thunderbolt 4 support last fall in the latest versions of the Asus ZenBook 13 (UX325EA) and the Dell XPS 13 (9310). More are sure to follow, but not every Tiger Lake laptop with USB-C ports will offer Thunderbolt 4 support. Look at the spec sheets carefully, as well as for the Thunderbolt logo, because without it you are likely staring at a vanilla USB4 port, which offers previous-generation Thunderbolt 3 capabilities.
Apple’s new M1 MacBook Air, MacBook Pro, and Mac mini were released near the end of 2020, and while these new systems feature USB4 ports, they do not offer formal Thunderbolt 4 support (just Thunderbolt 3). It remains to be seen when the first Mac with Thunderbolt 4 will arrive, and whether it’ll show up on a Mac with Apple’s own M1 silicon or a Mac based on Intel Tiger Lake CPUs.
On the peripheral side of the fence, the very first Thunderbolt 4 docks were starting to hit the market with announcements at CES 2021 (see this example from Kensington and another from OWC), while hubs, external drives, external GPUs, and displays seem imminent. You can be certain they will start rolling out later this year as more PCs and laptops with Thunderbolt 4 are released.
