For the uninitiated, both USB-C and Thunderbolt 3 are the same, as they both have a bi-directional connector, meaning you can't go wrong connecting a cable. But there is a difference between the two.
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Under the name of Thunderbolt is a very notable hardware interface in the world of computing. Allows you to connect peripheral devices to your computer. And the distinctive speed is the high data transfer rate - up to 40 Gb/s in the third version of the interface. By comparison, USB 3.0 offers a maximum speed of only 5 Gb/s, depending on the specification. Apple was behind the interface and it is still used today more than any other manufacturer. When describing brand-name computers, Thunderbolt is often mentioned, but what it is and how it works is not widely understood.
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It's important to know that Thunderbolt is built on top of PCI Express (PCIe) and DisplayPort. This is why Thunderbolt 3 cables and accessories are not compatible with "pure" USB-C ports (or rather, most of them, later).
The Thunderbolt interface was developed in the 2000s in an active collaboration between Intel and apple. The technology was originally designed to work with optical cables and was called Light Peak. But it turned out that even a cheap regular copper connection could deliver the specified speeds. In addition, the copper cable was capable of transmitting power: the latest standard was up to 100 W per port.
Light Peak technology was introduced by Intel in 2009: a 30-meter optical cable is used to transmit two high-resolution video streams. And the first commercial device to use this interface (renamed Thunderbolt) was the MacBook Pro, announced in early 2011. A market for Thunderbolt-compatible peripherals gradually emerged. The second version was introduced in 2013, but current Apple devices already use Thunderbolt 3.
PCIe offers enormous Bandwidth: large amounts of data pass through several communication channels at the same time. That's why Thunderbolt 3 is so fast. But that also means that for Thunderbolt 3 accessories, only the Thunderbolt 3 port is suitable. Why? Because USB-C does not use PCIe in its operation. So if you plug a Thunderbolt 3 accessory into a USB-C port, it simply won't work because the USB-C port doesn't have a PCIe controller.
In other words, Thunderbolt 3 has additional "hardware" compared to USB-C, more "current" and therefore simpler. It's important to know that USB-C cables and accessories are compatible with Thunderbolt 3 ports.
All Thunderbolt 3 ports are also USB-C ports. But the opposite statement is incorrect: not all USB-C ports are Thunderbolt 3 ports.
Admittedly, there's a nice "but" here... Yes, you can't use most Thunderbolt 3 devices with a USB-C port. But the opposite is true: you can connect a USB-C device to Thunderbolt 3 because Thunderbolt 3 is fully compatible with USB-C. So if you connect a USB-C hard drive to your MacBook Pro, for example, everything will work without a problem. In other words, this issue is irrelevant to Mac owners: all USB-C peripherals are supported.
And here's the other thing: things got more complicated (but also nicer) in early 2018. The thing is, Intel introduced a new controller for Thunderbolt 3 called Titan Ridge. It still has Thunderbolt 3 (40Gbps) bandwidth, and compatible accessories now support USB-C. This means that accessories with the Titan Ridge Thunderbolt 3 controller will be functional when connected to the USB-C port. Yes, the speed won't be the same, but it's better than nothing. Another thing is that nobody specially advertises this feature, so you will have to do some research before buying one accessory or another.
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Advantages of Thunderbolt 3
Thunderbolt 3 is by far the most powerful and versatile port on the market today. Compared to the previous version of the interface, the transfer speed has been doubled. Thunderbolt 3 lets you connect docking stations, monitors, laptops, and other accessories together very quickly.
Another advantage of Thunderbolt 3 over USB-C is the ability to daisy chain. Up to 6 peripheral devices (such as monitors or external storage devices) can be connected to this connector, connecting them together with cables. All daisy chained devices will be available for use on your Mac. USB-C does not have this option.
Bands' high width lets you connect four 4K or two 6K monitors to your Mac at once. Needless to say, it's Thunderbolt capability that enables these professional solutions. And for professionals who process photos and videos, it's a feast for the senses. And the MacBook Pro 16 even includes two. And Thunderbolt 3 lets you connect DisplayPort monitors directly, while HDMI/VGA connectors require an adapter.
Transmission speeds are so fast that it takes less than a minute to copy 14 hours of HD video. It takes the same time to transfer 10.000 music tracks or 25.000 photos.
Not only can you transfer video and data, but you can also charge your devices through a single compact connector. The current implementation uses a USB-C interface, which is very easy to use. Energy can be transmitted through it in two directions. That is, both the connected device and the device connected to it can be recharged. In total, Thunderbolt 3 supports up to 100 watts of power, allowing you to connect multiple powerful devices via a single cable and recharge them at the same time.
Using the USB-C interface makes Thunderbolt 3 a truly versatile solution. Now you can connect almost any device to the port with a single cable, but Thunderbolt 2 devices will require an adapter. Now it's much easier to connect Apple Thunderbolt 3 devices and iOS / iPadOS devices together. The USB-C port is great for connecting the many modern accessories and external storage devices. Adapters and adapters will continue to be required to connect to the legacy interfaces, but compatibility between the two has been maintained.