At first glance, it's hard to tell the two apart. Both share the standard USB-C connector, and both have a top speed of 40Gbps. In theory, a Thunderbolt 3 device should be able to do just about anything a Thunderbolt 4 device can do. Confused yet? You're not alone.
We've already established USB was originally conceived to combat connection confusion. So how does adding Thunderbolt to the mix help? It doesn't. At least, not at first.
Compared to version 3, Thunderbolt 4 requires a much stricter set of capabilities to be certified. Take video for example. Every Thunderbolt 4 laptop supports two 4K displays or one 8K display. By contrast, Thunderbolt 3 is only required to support one 4K monitor. So some Thunderbolt 3 ports support two displays at 4K or even one at 8K while others only support one 4K monitor. This gives the manufacturer more flexibility in design and build, but it also makes things very confusing for the customer.
You can see similar trends in data transfer. Thunderbolt 4 requires PCIe at 32 Gbps for storage speeds up to 3,000 MBps. Double the minimum requirements of Thunderbolt 3.
Unlike Thunderbolt 3, the ability to wake a computer with the shake of a mouse or the tap of a keyboard is now standard on Thunderbolt 4 docks. A small requirement, but one that relieves a lot of annoyance for the end-user.
Thunderbolt 4 also works harder to keep your data safe by requiring Intel VT-d-based direct memory access (DMA) protection.
At Plugable, we're most excited about support for docks with up to four Thunderbolt 4 ports and universal 40Gbps cables as long as 2 meters.
Thunderbolt 4 is fully compatible with prior generations of Thunderbolt and USB peripherals, though you will need to account for the different connector types.