The modern world runs on USB, also known as Universal Serial Bus. Whether it's the old-school USB-A ports built into hotel lamps or high-powered Thunderbolt powering entire workstations, USB is still how we all charge and connect our devices.
Unfortunately, as its importance has grown over the years, so has its complexity. What's USB4? How about Thunderbolt? Is it the same as USB-C? Knowing the subtle differences between these will help guarantee that you're getting the most out of your devices and peripherals.
Updated September 2025: We've rewritten much of this guide to improve clarity and brought it up to date with new sections on DP Alt Mode and USB-PD.
USB-C, USB-A, and More
USB-C or USB-A refer to the physical shape of the connectors and ports on devices, not necessarily their speeds or features. Since its invention in 2014, USB-C has slowly overtaken USB-A and become more common as it's smaller and more powerful. The shape resembles a small, elongated oval, unlike the rectangular shape of USB-A. USB-C is also reversible, so you can't plug it in the wrong way.
Beyond that, though, there are also hardware limitations in the design of USB-A, which has a fixed 5-volt power delivery that USB-C doesn't have. More on that later with USB Power Delivery and DisplayPort Alt Mode, which greatly expand what USB-C can do today.
Outside of USB-C and USB-A, there are a lot more types of USB connectors, some of which you will still run into on older accessories, such as USB-B and Micro-USB. For example, I have a pair of older on-ear headphones that still charge via Micro-USB, while a MIDI keyboard has a USB-B port type. These both use USB-A on the other end, but still represent assorted port types you'll encounter that require different cables. Fortunately, many of these are moving to USB-C, which is a more universal and capable standard in charging adapters, hubs, and docking stations today.
What Is Going on With USB Generations?
Whether it's USB-C or USB-A, every USB device is built on some version of the USB specification, managed by the USB Implementers Forum (USB-IF). These versions are mainly characterized by how much data they can transfer and how much power they can deliver (at least, those are the main things you need to care about).
While most of these devices are interoperable as long as they use the same type of port, the entire chain will conform to the slowest part of the chain. Say you plug a USB 3.2 solid-state drive into a USB 3.2 port on your computer, but use a USB 3.0 cable. Unfortunately, this will mean that data will only transfer at USB 3.0 speeds. So, if you want that full speed, you'll need to make sure every link in your chain is rated for the speed you need.
The latest version is USB4, which has been around since 2022. It was initially capable of speeds ranging from 20 Gbps to 40 Gbps, which doubles the bandwidth over USB 3.2 Gen 2. It's the first generation of USB to be built exclusively for USB-C, meaning all future advances will be leaving USB-A behind. USB4 Version 2 was announced and certified back in 2022, bringing potential speeds up to 120 Gbps (Gigabits per second), but devices and peripherals have still not widely adopted it.