About Thunderbolt 4 (Updated)

KALM-150x150"Tom provides a brief explanation of Thunderbolt 4 and its similarities, and differences, to previous Thunderbolt standards. Updated to include Apple M1 compatibility.

Featuring Tom Merritt.



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Episode Script
It’s faster right?
No? But it’s better than USB 4. Maybe?
Wait the cable and the port look exactly the same as Thunderbolt 3 and USB! What is going on here?
Let’s help you Know a Little More about Thunderbolt 4.
First let’s start with what Thunderbolt is.
Thunderbolt is a brand name. It’s a hardware interface developed by Intel in collaboration with Apple.
It’s essentially a protocol for transferring data, implemented in some specialized controller hardware inside your computer and its connected devices.
These days it’s easy for a user to confuse it with USB-C because it uses the same connector. Old time Thunderbolt users will remember that Thunderbolt 1 and 2 used the DisplayPort connector. Thunderbolt 3 and 4 use USB-C.
But it’s not USB. It actually combines PCI express or PCIe and DisplayPort and provides DC power. Though– it also supports USB if you need it. So its USB plus a lot more.
Thunderbolt can handle up to 6 connected peripherals through one port. You do that with a combination of hubs or devices by connecting each Thunderbolt device to the other until the last one in the chain connects to the computer. So let’s say you have a drive and an external GPU connected to a two port Thunderbolt 3 hub connected to another drive connected to a display with two ports connected to a computer. Stuff like that.
So what does Thunderbolt do?
To oversimplify it takes the data from each device in a few lanes then sends them — or multiplexes them– to the computer. At the other end the Thunderbolt controller de-multiplexes them and sends them along to to the PCIe or DisplayPort hardware in the computer. Like a PCIe graphics card for instance.
The original thunderbolt cables carried four lanes of data. Two of them for output and two for input. Each pair of output and input lanes handled up to 10 Gbps.
Originally Thunderbolt cables were all optical fiber. You may recall Thunderbolt was originally marketed as LightPeak. Eventually they figured out how to do the same speed over copper which was cheaper, so most current Thunderbolt cables are copper.
That’s where Apple came in. It co-developed the copper version with Intel and originally Apple registered the Thunderbolt trademark which it transferred to Intel.
Intel is still developing an optical version of Thunderbolt along with Corning. You can buy optical Thunderbolt 3 cables up to 30 meters long aka 100 feet. They are not cheap though.
OK so Over the course of developing Thunderbolt the specs increased.
Thunderbolt 2 allowed the 2 10 Gbps duplex lanes to be used together to achieve 20 Gbps through something called channel aggregation, though the actual bandwidth was technically the same as Thunderbolt 1. The higher achievable speed allowed it to handle 4K video.
Thunderbolt 3 changed from using the DisplayPort connector to using the USB-C connector. It was able to handle 4 10 Gbps lanes increasing the maximum bandwidth to 40 Gbps. And in addition to PCIe and DisplayPort it added support for USB 3.1 at 10 Gbps.
Thunderbolt 3 also needed half the power of Thunderbolt 2 allowing it to drive two 4K monitors at 60 Hz. Though a manufacturer didn’t have to support two 4K displays so not all Thunderbolt 3 ports did. It also increased power delivery from 10 to 15 watts AND with USB Power Delivery it could source or sink up to 100 watts.
Special active cables were needed for cables more than half a meter or 1.5 feet, though less expensive USB-C cables can be used on Thunderbolt 3 ports they just don’t get the full speed benefit though it is slightly faster than USB 3.1.
In 2018 Intel released Thunderbolt 3 royalty free and on March 4 2019 it was released to the USB Implementers Forum (USB-IF) to be used royalty-free as the basis for USB 4. The USB 4 spec was released in August 2019 based on the Thunderbolt 3 spec, though Thunderbolt 3 continues to only support USB 3.1.
That brings us to Thunderbolt 4. Its spec was released in July 2020.
It is backwards compatible. All Thunderbolt 3 cables and accessories will work with Thunderbolt 4. And Thunderbolt 4 supports USB 4 which is backwards compatible with previous USB.
Otherwise Thunderbolt 4 takes a lot of things that Thunderbolt 3 could do but didn’t always and makes them mandatory.
Thunderbolt 4 implementations must support dual 4K displays (remember Thunderbolt 3 could– but the manufacturers didn’t have to and often didn’t) Thunderbolt 4 also supports one 8K display.
It requires Intel’s Direct memory Access protection, known as Virtualization for Directed I/O or VT-d. This creates a separate memory pocket for your transferred data. That means someone with physical access to your machine can’t plug something into the Thunderbolt port and read what’s in memory and steal your encryption keys or gain access and install malware.
The bandwidth for Thunderbolt 4 remains at 40 Gbps BUT you might still see a boost since Thunderbolt 4 supports PCIe bandwidth of 32 Gbps, twice what Thunderbolt 3 supported. Some Solid state drives support this too, meaning some data retrieval and storage could be faster over a Thunderbolt 4 cable. Great for video transfer say.
You may wonder why you need 40Gps on your Thunderbolt cable if PCIe can only do 32Gbps. And it’s a good question. Remember you can daisy chain stuff. Put one 4K display a USB 3.1 device and ethernet all on one Thunderbolt 4 port and you would use just a bit more than 25 Mbps. Add a second 4K display to that daisy chain and you’ve maxed out at 40gbps. So that 32Gbps PCIe device will likely have to be on a thunderbolt port alone if you want full speed.
Oh and full speed can happen over a cable up to 2 meters long now.
Thunderbolt 4 also supports accessories having four Thunderbolt ports themselves. Thunderbolt 3 docks could only do two.
Thunderbolt 4 requires wake from sleep when a computer is connected to a Thunderbolt dock. So you touch the keyboard or mouse and it wakes up. (Yeah Thunderbolt 3 didn’t require this)
And any computer that wants Thunderbolt 4 certification must make at least one of the Thunderbolt 4 ports a charging port up to 100 watts.
So how do you get it? You probably buy a new computer.
To get Thunderbolt 4 you’ll need a computer that has it, which will usually come along with Intel’s Tiger Lake chip. Apple supports Thunderbolt 4 on its machines that use the M1 ARM-based Apple Silicon.
How can you tell if a computer has Thunderbolt 4? Not easily. The port looks just like USB-C. Thunderbolt ports have a lightning logo by them but that doesn’t tell you which version. So you’ll have to dig into a machine’s specs in the OS or on the box. Cables on the other hand will have the lightning bolt symbol and the number 4.
So do you need Thunderbolt 4? Well if you want to make sure you can handle two 4K monitors yes. Or if you transfer a lot of data from external drives, like for video editing and want that faster data transfer, yes. Otherwise it’s at best a nice to have.
And it’s still confusing, port and cable wise since all these ports and cables look the same now. But I hope we helped you reduce that confusion just a little.
In other words, I hope you Know a Little More about Thunderbolt 4.