Why do some USB ports have a circular symbol?

We may receive a commission on purchases made from links.

To find the ideal USB port for a specific purpose, you can experiment by plugging the connector into different ports, or you can simply look at one of the many indicators that tell you precisely which port version and what capabilities you’ll get. Of course, USB Type-C ports are very different from USB Type-A, but each of these port standards has several versions. To tell them apart, you can look at the color (each type of USB port has a different color) or you can look at the symbol next to the port, if there is one available. These symbols include the standard USB trident, the trident with variations such as “SS” or numbers, a lightning bolt, and, on newer ports, a circle with a number – technically a semi-circle. This circular symbol, which surrounds a number like 20 or 40 and has a USB trident protruding from one side, indicates a USB4 port.

USB4 is one of the newer specifications and uses the USB Type-C form. The reason this distinction is important is because, again, there are multiple versions of USB-C, each with unique capabilities. USB4 supports higher data transfer speeds and higher power delivery, often indicated by the number on the symbol. A circle with a 20 tells you it’s a USB4 port capable of handling speeds of up to 20 Gigabits per second (Gbps), while a circle with a 40 tells you it can handle almost double that, up to 40 Gbps. USB4 also natively supports the PD standard for fast charging, with up to 240 watts of power.

If you see the circle or semi-circle icon with a number, that’s the port you want to use for data transfers and delivering high power. Note that you will also need a compatible cable; USB cables often have the same symbols printed on them, and if not, the manufacturer often lists specifications, such as maximum data transfer rates and power output capabilities. This is why you want to avoid cheap or generic USB cables, and also why it’s not really safe to charge your phone or devices with a cheap USB cable either.

There is another circular symbol that may appear near USB ports. It is the symbol of power – a circle with a line through it. If and when you see a power symbol near a USB port, often right next to the USB trident, it means the port is always on, so it will charge and power devices even when the main computer or system is off, because it still has power. Teal, red, and yellow colors on the USB ports can also indicate an always-on charging port. Learning the symbols, colors, and different indicators will really help you navigate the world of USB standards and specifications, which admittedly can get quite confusing at times.