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Definition: USB

(1) See USB drive and USB port.

(2) (Universal Serial Bus) A hardware interface that supports up to 127 peripherals. USB is used to attach keyboards, mice, printers, external storage and mobile devices to the computer. It is also used for charging portable products (see USB power). Governed by the USB Implementers Forum (see USB-IF), USB emerged in the mid-1990s and soon replaced all earlier ports (see serial port, parallel port and Apple Desktop Bus).

Hot Swappable Drives
USB devices can be plugged and unplugged while the computer is on. However, thumb drives require a software "eject" beforehand. 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.

SuperSpeed Logos
As of USB 4, the nomenclature was simplified so that future SuperSpeed logos show their speed ratings (5, 10, 20, 40) and eventually replace the multiple designations for USB 3.x (see USB 3.2). DisplayPort requires USB-C cables (see USB Type C).

 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

 USB 4                  40 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 to transmit the video signal it receives, but its power comes from USB (see Chromecast and USB power). (Image courtesy of Google Inc.)