Learn to untangle USB and Thunderbolt cables

Digging into these multi-purpose standards can help you troubleshoot problems and obtain your best connection rates.

- GLENN FLEISHMAN

One of the world's least exciting sentences is, "Let's talk about technology standards!" But I promise I'm not digging down into wiring schematics, pinout diagrams, and 1,000-page protocol descriptions. Rather, I want to help you get up to speed on how USB and Thunderbolt work separately and together so you know how you can best use them and troubleshoot them when incompatibilities arise.

The path forward relies on the latest standards: Thunderbolt 4 and USB4. While not perfectly compatible with each other, they are nearly so. Most importantly, the two standards have effectively converged on a single cable type you can purchase and use almost universally with Thunderbolt 3 or 4, and USB 3.1, 3.2, and USB4 via USB-C.

USB: THE ONCE AND FUTURE UNIVERSAL STANDARD

USB was at one point the great hope of the future: Universal! Serial! Bus! All three words pointed in the right direction. Instead of many serial connectors and buses (and even some parallel ports), USB would unify many kinds of purpose into one controller with a limited set of jacks and plugs designed for different purposes. All USB devices could plug into any USB port, given the right cable.

A lovely idea, but one that was ruined by the large number of USB plug types that emerged. There are currently nine kinds of USB connectors. But that's not the only issue: even though you may be most familiar with the rectangular USB Type-A plug and jack, a USB cable cannot have a Type-A plug on both ends, whether full-sized, Mini, or Micro.

In a chart from Wikipedia's extensive USB entry (fave.co/3LM61eL), shown below, the eight kinds of USB connectors run across the top and down the side. The following points are worth noting:

> Type-A can't connect to Type-A: it's noted as "Proprietary, hazardous"