USB Type-A connectors, officially called Standard-A connectors, are flat and rectangular in shape. Type A is the “original” USB connector and is the most recognizable and commonly used connector. USB Type-A connectors are supported in every USB version, including USB 3.0, USB 2.0, and USB 1.1.
One of two standard USB connectors, the USB Type B connector (technically known as a “Standard B” connector) is roughly square in appearance, with a squarish protrusion on top. Type B ports are found on many USB non-host devices, such as audio interfaces, external hard drives, and printers.
The USB 3.0 Micro B connector is found on USB 3.0 devices. This connector is designed to carry data and power in USB SuperSpeed applications. Cables with this connector are not backwards compatible with USB 2.0 or USB 1.1 devices.
USB-C is a 24-pin USB connector system with a rotationally symmetrical connector. The USB Type-C Specification 1.0 was published by the USB Implementers Forum and was finalized in August 2014. It was developed at roughly the same time as the USB 3.1 specification.