The USB 1.0 standard was released in January 1996 and updated to 1.1 in August 1998. USB 1.0 data rates of 1.5 Mbit/s (Low Speed) and 12 Mbit/s (Full Speed). While communication is bidirectional, data transfers are half-duplex (only one direction at a time). Few USB compatible devices were released until the 1.1 specification. Both USB 1.0 and 1.1 use the Type A and Type B connectors.
The 2.0 specification was released in April 2000. This specification increased the data rate to a theoretical maximum of 480 Mbit/s but remained half-duplex. Introduced along with USB 2.0 were the USB Mini and Micro connectors. USB 2.0 is backward compatible (a USB 1.1 peripheral can be used with a computer that has a USB 2.0 port) with USB 1.0 & 1.1 devices.
The USB 3.0 standard was released in November 2008. The 3.0 standard increased the theoretical maximum speed of USB to the ‘SuperSpeed’ rate of 5.0 Gbit/s. Data communication was also upgraded to full-duplex (both directions at the same time). Connectors for 3.0 connections are distinguished by their blue inserts for the standard Type A connectors.
In July 2013 the standard was upgraded again to 3.1. The 3.1 standard further increased the speed of USB to the ‘SuperSpeed+’ theoretical maximum rate of 10 Gbit/s. The Micro B SuperSpeed connector was introduced.
In September of 2017, the most recent upgrade to the standard was released with USB 3.2. Two new SuperSpeed+ transfer modes were introduced both using the USB Type C connector. These new SuperSpeed+ modes provide a maximum theoretical data transfer rate of 10 and 20 Gbit/s respectively.
USB 3.x is backward compatible with USB 1.0, 1.1, and 2.0 devices. Backward compatibility means that the connection will function at the speed of the slowest component. To achieve the best performance the peripheral, cable, and computer port must be compatible with the same USB standard.
Announced by the USB Promoter Group on March 4, 2019. Expect speeds up to 40 Gbit/s, though the standard has not yet been released.