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Definition: USB

(1) See USB drive and USB port.

(2) (Universal Serial Bus) USB is a hardware interface for up to 127 peripherals that is governed by the USB Implementers Forum (see USB-IF). USB is used to attach keyboards, mice, printers, external storage and mobile devices to the computer. It is also used for charging a wide variety of portable products (see USB power). After debuting in 1997, USB soon replaced the earlier serial port, parallel port and Apple Desktop Bus.

Hot Swappable Drives
USB devices can be plugged and unplugged while the computer is on. This feature, combined with easy-to-reach ports on every computer, gave rise to the ubiquitous USB drive for transport (a manual "eject" is however required). See USB drive, USB device class, USB OTG, USB switch and USB toy.

Connecting via USB
Host sockets are Type A, and peripherals use B, Micro-B, Mini-B, USB-C and Lightning. In time, USB-C is expected to replace A, as well as every other USB connector. Today, some laptops have only USB-C ports, while all other computers have Type A. See USB Type C, USB hub, Mini USB, Micro USB and Lightning connector.

Officially USB 2.0 and 3.2
Although USB 2.0 and 3.2 are the only official versions, the previous USB numbers are widely used, creating several a.k.a. versions. The above logos must be licensed by the USB Implementers Forum. However, the SS20 logo was added for continuity but was not official when this illustration was created (see below). DisplayPort requires USB-C cables (see USB Type C). See USB-IF and USB 3.2.

 USB 2.0              Data Rate

 USB 2.0 High Speed    480 Mbps
 USB 2.0 Full Speed     12 Mbps
 USB 2.0 Slow Speed    1.5 Mbps

 USB 3.2              Data Rate  Lanes

 USB 3.2 Gen 1x1         5 Gbps   1
 (a.k.a. USB 3.0)
 (a.k.a. USB 3.1 Gen 1)

 USB 3.2 Gen 2x1        10 Gbps   1
 (a.k.a. USB 3.1
 (a.k.a. USB 3.1 Gen 2)

 USB 3.2 Gen 1x2**      10 Gbps   2
 USB 3.2 Gen 2x2**      20 Gbps   2
 ** Dual-lane requires USB-C cables

USB Is Often Power Only
USB is widely used as a power source for phones, tablets and other devices. This Chromecast streaming stick plugs into the TV's HDMI port but is powered by USB (see Chromecast and USB power). (Image courtesy of Google Inc.)