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The difference between USB-C™ and Thunderbolt™ 3

USB Type-C or for short USB-C is a specification for connectors and cables. It's a small and reversible connector. Thunderbolt 3 defines a superset of capabilities that runs on USB-C connectors and cables. At 40 Gbps, Thunderbolt 3 is currently the fastest connection available for Akitio's storage solutions.

When choosing a computer or a device with USB-C ports, always check the specfications first. Even though a Thunderbolt 3 capable computer with a USB-C port is backwards compatible with USB devices, it does not work the same the other way around. If the computer has a USB-C port supporting only USB 3.1 Gen 1, USB devices with a USB 3.1 Gen 2 interface will be limited to 5 Gbps only and Thunderbolt 3 devices will not be compatible at all.

USB drives

Almost every computer has a USB port, making USB the ideal interface for drives that are used on more than just your own computer. For single HDDs, even the first generation of USB 3.1 (USB 3.0) is fast enough and will not limit your transfer rate. For SSDs, it's best to use the second generation of USB 3.1 at 10Gbps but for multiple drives, the transfer rate will be limited to around 700-800 MB/s and that's with the faster USB 3.1 Gen 2 interface.

Thunderbolt drives

With Thunderbolt 3, currently the latest generation of the Thunderbolt interface, you get plenty of bandwidth even for multiple drives and when daisy chaining additional Thunderbolt drives. The bottleneck of the Thunderbolt 3 interface is at around 2750 MB/s but for now, only certain NVMe SSDs can reach these kind of speeds, so in most cases, the transfer rate will not be limited.

With Thunderbolt 2, the bottleneck is at around 1375 MB/s. This kind of bandwidth is ideal for up to 4 SATA-III drives but it's not fast enough for an NVMe based SSD and even four SATA-III SSDs can be limited by this interface.

The first generation of Thunderbolt is similar to the USB 3.1 Gen 2 interface. The transfer rate will be limited to around 700-800 MB/s, which is ideal for multiple HDDs or 1-2 SSDs but not for more than 2 drives.

USB 3.1 Gen 1 ~300-400 MB/s Available on most computers Not fast enough for faster drives
USB 3.1 Gen 2 ~700-800 MB/s Fast enough for 1-2 SSDs Not fast enough for more than 2 drives
Thunderbolt ~700-800 MB/s Fast enough for 1-2 SSDs Not fast enough for more than 2 drives
Thunderbolt 2 ~1375 MB/s Fast enough for 3-4 SSDs Not fast enough for NVMe based SSDs
Thunderbolt 3 ~2750 MB/s Enough bandwidth even when daisy chaining multiple devices Not fast enough for certain NVMe based SSDs (e.g. Samsung 960 Pro)

USB-C cables and adapters

For slower interfaces like USB 3.1 Gen 1, the cable usually doesn't affect the transfer rate, so any cable will work. For faster interfaces like USB 3.1 Gen 2 and Thunderbolt, the type and quality of the cable can affect not only the transfer rates but also the functionality, so it's important to always use the cables that came included with your product or high quality alternatives.

When buying a different cable, as a general rule, the shorter and thicker the less problems and the longer the cable gets, the more likely the quality can affect the speed or functionality. Special care has to be taken when buying an adapter plug or a cable to convert one type of connector to another (e.g. USB-C to USB Type A). A bad adapter can cause the drive to lose connection and some adapters are not designed to handle the faster transfer rates of interfaces like USB 3.1 Gen 2 or Thunderbolt 3 for example.

USB 3.1 Gen 1 cable 5Gbps Low cost and commonly available Slow transfer rates and doesn't work with Thunderbolt 3 devices
USB 3.1 Gen 2 cable 10Gbps Fast transfer rates Expensive and doesn't work with Thunderbolt 3 devices
20Gbps Thunderbolt 3 cable 1m/2m 20Gbps Relatively long cable Reduced transfer rates
40Gbps Thunderbolt 3 cable 0.5m 40Gbps Fast transfer rates and compatible with Thunderbolt 3 & USB-C devices Short cable
40Gbps Thunderbolt 3 cable 1m/2m 40Gbps Fast transfer rates and relatively long cable Works only with Thunderbolt 3 computers and devices

Frequently asked questions

Can I connect a Thunderbolt 3 device to a USB-C only computer?
No, to use a Thunderbolt 3 device, a Thunderbolt 3 capable computer is required.

Is there an adapter to connect a Thunderbolt 3 device to a computer without Thunderbolt?
No, a Thunderbolt 3 capable computer is required but if you are using a Thunderbolt (1) or Thunderbolt 2 Mac, you can use the Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter from Apple to connect the Thunderbolt 3 device to your Mac.

Can I use a USB-C to USB Type-A adapter cable to connect my USB-C drive to an older computer?
Yes but please keep in mind that not all adapters are built the same and if possible, it's best to test the adapter first, before using it in a production environment. Possible problems with a low quality adapter could be slow transfer rates, compatibility issues, insufficient bus-power or loss of connection and/or data.


Thunderbolt and the Thunderbolt logo are trademarks of Intel Corporation in the U.S. and other countries.
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USB Type-C and USB-C are trademarks of USB Implementers Forum.
Other names and brands may be claimed as the property of others.