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Definition: USB


(1) See USB drive and USB port.

(2) (Universal Serial Bus) USB is the most widely used hardware interface for attaching peripherals or a mobile device to a computer. USB designations use a letter and number such as Type A 3.0. The letter is the type of connector, and the number is the speed (see below). The latest Type C was designed to replace all previous connectors (see USB Type C).

Computers Have Type A
Although Type C should eventually replace Type A, there are generally at least two Type A ports on laptops and four on desktops, while USB "hubs" provide even more (see below). After debuting in 1997, USB became the standard for connecting keyboards, mice, printers and external storage drives, eventually replacing the PC's serial and parallel ports and the Apple Desktop Bus on Macs (see serial port, parallel port and ADB).

Hot Swappable USB Drives
Supporting 127 devices, they can be plugged and unplugged while the computer is on. This "hot swappable" 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. See PoweredUSB, USB device class, USB OTG, USB switch and USB toy.




Type A and B Ports
Host sockets are Type A, and peripheral sockets are B, C and Lightning. Type C is expected to eventually replace the A-B connection (see USB Type C). See USB hub, Mini USB, Micro USB, Lightning connector and USB OTG.

 USB                  Transfer
 Version (Year)         Rate      Amps

 SuperSpeed+ (2014)
 USB 3.1 Gen 2        10 Gbps      5 A
 See USB 3.1.

 SuperSpeed (2008)
 USB 3.1 Gen 1
 a.k.a. USB 3.0        5 Gbps    900 mA
 See USB 3.0.

 Hi-Speed (2001)
 USB 2.0             480 Mbps    500 mA

 USB (1998)
 USB 1.1         Slow  1.5 Mbps
                 Fast 12.0 Mbps
 (Slow channel for keyboards, mice, etc.)












USB Can Be Power Only
USB is also a power source for phones, tablets and other devices. This Chromecast streaming stick plugs into the TV's HDMI port but is powered from a USB port (see Chromecast). (Image courtesy of Google Inc.)