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July 20, 2021
Thunderbolt 4
Is it the crowning "one wire" connectivity and charging answer to the increasingly fragmented USB landscape?
by Conrad H. Blickenstorfer
With computers, no matter what kind of computer, connectivity is everything. If there's no cell service or no WiFi, one is disconnected from the world. And it's pretty much the same with wires and cables. Unless you have the right ones with the right plugs you're out of luck.
That was a very big deal in the early days of PCs when PCs and peripherals connected either with a serial or a parallel cable. That sounds simple, but it wasn't. While the connectors were more or less standard, different companies often assigned different functions to different pins and one needed a special "driver" to make it work. Sometimes dip switches were involved or little adapter boxes where you could set the proper connections between all the wires.
That went on for a good decade and a half after PCs first appeared. In the mid 1990s USB, the Universal Serial Bus, appeared and promised to put an end of all that incompatibility and frustration. The intent of USB was to bring simple "plug and play" functionality. If the PC and the peripheral both had USB ports, you simply connected them and it worked. In real life it wasn't that easy. USB, too, needed drivers and it took a good many years for most things to be truly "plug and play."
USB now
It's now a quarter of a century later and USB is still with us. USB is everywhere. The Universal Serial Bus has indeed become universal. Pretty much every device has one or more USB ports.
And yet, USB isn't really completely universal. As technology advances and makes computers more and more powerful, the original USB standard soon was no longer quick and flexible enough to meet emerging demands. The original USB 1.0 standard wasn't very fast and could only transfer in one direction at a time. USB 2.0 was faster but still couldn't transmit data both ways simultaneously.
That was fixed in USB 3.0 (you can tell that a USB port is version 3.0 or better by its blue plastic tab inside the connector) and USB 3 also went from just four wires in a cable to nine. USB 3.0 was also faster and could transmit video. USB 3.1 was faster yet, up to 800 times as fast as the original USB port. But why stop at that? And so USB 3.2 was up to twice as fast as USB 3.1.
But speed was not all that came with USB 3.1 and 3.2; they also fixed one of the inherent nuisances of the original USB concept: you could only plug it in one way. So since USB ports are often in fairly inaccessible and/or dimly lit locations, one had a 50% chance of successfully plugging a cable in on the first try. Very frustrating. That's now changing with the USB Type-C port. The Type-C plug is not only smaller and has new pins for even more functionality, it doesn't matter which way you plug it in because it has a duplicate set of those pins.
Conceptually, the combination of the reversible Type-C plug and the great speed of the USB 3.1 and USB 3.2 standards is a big step forward. The problem is just that there are still billions and billions of older plugs (including USB Type B and the various mini and micro USB plug versions), which means having the right cable with the right plugs on either end remains a very real problem.
But wait, there's more. Apple has always done things differently and that includes ports and interfaces. Sometimes Apple yielded when staying with proprietary technologies became too much of a limitation (as was the case with adopting USB), but often Apple doesn't shy away from using less common but faster and more powerful interfaces.
Thunderbolt
Thunderbolt, a joint effort between Intel and Apple, is one of them. About a decade ago Apple began adding Thunderbolt ports. The first two versions, Thunderbolt 1 and Thunderbolt 2 sort of combined the PCI Express and DisplayPort signals and used a unique (and non-reversible) connector. Thunderbolt 3, which boosted the speed and capabilities of PCIe and DisplayPort, switched to using the USB Type-C connector. The latest version, Thunderbolt 4, again uses the USB Type-C connector, but supports USB 4 with up to 40 Gbit/s (5 GB/s) throughput as well as dual 4K displays. Thunderbolt 4 cables can be up to two meters (6.6 feet) long whereas the USB 4 limit is less than three feet.
So now we have a situation where USB 4 mandates the USB Type-C port, supports PCI Express and DisplayPort, and can (but does not have to) support the same high 40 Gbit/s throughput. Both use the USB Type-C port and the same standards. So what's different?
Well, anything named Thunderbolt must be fully certified to pass all of the required Thunderbolt features and speeds. USB 4, on the other hand, only supports one display, may support only lesser speeds, and USB 4 devices do not need to be certified.
So what does all of that mean to you, the consumer? For the most part, laptops and tablets will continue to have the standard Type-A USB port. Depending on the device, those may be USB 2.0 or USB 3.0 ports, with the former having a black plastic insert and the latter a blue one. USB 3 ports will be listed as supporting one of the several USB 3.x version. Most new laptops and tablets will also have one or more USB Type-C ports and the specs will say what version and generation of the USB standard they support. So USB 3.1 Gen 1 would mean up to 5Gbit/s and USB 3.1 Gen 2 up to 10Gbit/s. With USB 3.2 it's always Type-C ports. Gen 1 and Gen 2 are the same 5 and 10Gbit/s, but there are now also Gen 1x2 and Gen 2x2 with up to 20Gbit/s transfer speed. Augh!
And there's more yet: There are also so called “alternate modes” in USB 3.1 and USB 3.2 that allow standard USB Type-C connectors to carry non-USB data by using some of the extra pins. These alternate modes may support DisplayPort, HDMI, MHL (Mobile High-Definition Link), Thunderbolt 3 or others.
And what can you expect from a USB Type-C port that is specifically labeled as Thunderbolt 4? Since Thunderbolt 4 must have minimum requirements certified, you get support of two external displays (up to 4k, or one 8k), 40Gbit/s data transmission, 32Gbit/s with PCIe, and 10Gbit/s with USB 3.2 connections.
Putting Thunderbolt 4 to the test
We put all this to the test with one of the early Thunderbolt 4 docks, the Anker PowerExpand 5-in-1 Thunderbolt 4 Mini Dock. It's a handy 5 x 3 x 0.75 inch box with three powered USB Type-C downstream ports, a 10Gbit/s USB Type-A port, and an upstream port to connect to the computer that delivers 
40 gbit/s data transfer, dual display support, and up to 85 watt charging power. It can do that by having its own and rather large 100 watt power brick.
We tried this with a Getac F110 tablet and a Getac K120 2-in-1, both new state-of-the-art rugged devices equipped with Thunderbolt 4 and running on Intel 11th gen Core processors, as well as a 2020 Apple MacBook Air.
Plugging the Anker dock into the Thunderbolt 4 port of the two Windows computers, we found the following:
What you can do with a PC’s USB-C Thunderbolt 4 port:
- Lets the PC drive a 2nd screen via USB-C to DisplayPort cable
- Lets the PC drive a 2nd screen via USB-C to HDMI cable
- Very fast file transfers (we used the Anker cable as well as an Accell USB4 40Gbps cable)
- Works with and powers external DVD reader
- Works with mice and keyboards
- Charges phones and tablets
What you can do with a Thunderbolt 4 dock connected to PC’s USB-C Thunderbolt 4 port:
- Drives two extra screens via USB-C or HDMI cables
- Works with USB docks
- Works with USB keys
- Works with and powers external DVD reader
- Works with mice and keyboards either through dock Type-A or Type-C ports
- Charges phones and tablets
What you don't necessarily get with Thunderbolt 4 is a guarantee that you can charge your device through the USB-C Thunderbolt 4 port. While Thunderbolt 4 cables can support up to 100 watts and the Anker dock can provide up to 85 charging watts, the Getac machines did not accept charging, even though the Anker power supply is actually rated at 100 watts. 
That’s because 15 watts of the dock’s power supply go to internal use and only 85 watts are available for upstream charging, and the Getac laptops want 90 watts. Charging the MacBook Air, on the other hand, worked fine. Discussion with Getac suggests that the Thunderbolt 4 "handshake" between the computer and the dock is such that if the wattage requirements are not met exactly, charging will not happen.
For now, Thunderbolt 4 doesn’t come cheaply. On the PC side it requires either a Thunderbolt controller or an 11th gen “Tiger Lake” mobile Core processor that already includes the Thunderbolt 4 controller. Docks also require a Thunderbolt controller, making it a higher-end feature, and that’s why even the small 5-in-1 Anker dock costs a hefty $200. For that it can charge and support phones as well as tablets and laptops (though that may depend on the individual device), provide very fast data transfer, support two external screens as well as whatever lesser USB keys, card readers or other peripherals you may want to attach to it. It did provide a true "one wire" solution for our MacBook, but, at least with the Anker 5-in-1 mini Thunderbolt 4 dock, not the two Windows computers which required more power than our test Anker Thunderbolt 4 5-in-1 dock could provide to allow upstream charging.
It is not immediately clear why Thunderbolt 4 should refuse charging unless a USB-C power source provides the same wattage as a laptops original charger. With a less powerful USB-C charger, charging might take longer, but so what?
As is, Thunderbolt 4 offers a lot, but sadly not a guarantee that everything works smoothly and effortlessly.
Addendum August 23, 2021:In the meantime we've had a chance to review another rugged mobile device built on Intel 11th generation Core processors and having a Thunderbolt 4 port. The semi-rugged Panasonic Toughbook 55 Mk2 could be charged both with the Anker 5-in-1 and the Anker 12-in-1 Thunderbolt docks.
I had also approached Intel's Thunderbolt 4 group with questions. Their response was:
"Thunderbolt charging is based on a robust, industry standard which is well adopted across the PC and Dock market and enables the PC and charger to negotiate to a variety of common charging levels. While Thunderbolt 4 can provide charge at multiple power delivery levels and many PC manufactures have chosen to support charging at multiple charging levels, some PC makers may choose to only support specific charging rates."
Posted by conradb212 at July 20, 2021 8:36 PM