USB 3.0 vs USB 2.0: Reference at a glance

The Universal Serial Bus (USB) has become the standard interface for connecting devices to a computer over the last 14 years. Whether it's an external hard drive, a camera, the mouse, a printer, or a scanner, the physical connection to transfer data between devices generally is a USB cable. The interface is indeed universal.

USB technology has been under development since 1993. The first official definition, USB 1.0, was introduced in 1996. It provides a Low-Speed transfer rate of 1.5 Mbit/s for sub-channel keyboards and mice, and a Full-Speed channel at 12 Mbit/s. USB 2.0, which came in 2001, made a leap to Hi-Speed transfer rates of up to 480 Mbit/s. In 2010, USB 3.0 finally hit the market. The table shows a summary of important specification differences between USB 2.0 and USB 3.0.

USB 3.0 (SuperSpeed USB)
USB 3.0 is the third major version of the Universal Serial Bus (USB) standard for computer connectivity. Among other improvements, USB 3.0 adds a new transfer mode called "SuperSpeed" (SS), capable of transferring data at up to 5 Gbit/s (625 MB/s), which is more than ten times as fast as the 480 Mbit/s (60 MB/s) high speed of USB 2.0. Besides different connectors used on USB 3.0 cables, they are also distinguishable from their 2.0 counterparts by either the blue colour of the ports or the SS initials on the plugs.

A successor standard named USB 3.1 was released in July 2013, providing transfer rates up to 10 Gbit/s (1.25 GB/s, called "SuperSpeed+"), which effectively put it on par with the first version of Thunderbolt.

USB 2.0 (High-Speed USB 2.0)
In 2002, a newer specification USB 2.0, also called Hi-Speed USB 2.0, was introduced. It increased the data transfer rate for PC to USB device to 480Mbit/s, which is 40 times faster than the USB 1.1 specification. With the increased bandwidth, high throughput peripherals such as digital cameras, CD burners, and video equipment could now be connected with USB. It also allowed for multiple high-speed devices to run simultaneously. Another important feature of USB 2.0 is that it supports Windows XP through Windows update.

Physical differences
The physical difference between USB 2.0 and USB 3.0 is the number of wire connections. This new topology greatly improves bus utilisation, resulting in improved system throughput. USB 2.0 uses four wires, which supports half-duplex communication. In this architecture, a single bi-directional data pipe is used where data only flows in one direction at any given time. In comparison, USB 3.0 adds five wires for a total of nine wires, and utilises a unicast dual-simplex data interface that allows for two uni-directional data pipes, with each pipe handling communication for a single direction.