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Definition: USB


(1) Short for "USB flash drive" or "USB port." See USB drive and USB port.

(2) (Universal Serial Bus) The most widely used hardware interface for attaching peripherals to a computer. There are at least two USB Type A ports on laptops and four on desktop computers, while USB "hubs" provide more connections (see below). After appearing 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).

Supporting 127 peripherals, devices can be plugged and unplugged while the computer is on. This "hot swappable" feature, combined with easy-to-reach ports on the front of the computer case, gave rise to the ubiquitous USB drive for transport, although a manual "eject" is required (see USB drive). See PoweredUSB, USB device class, USB OTG, USB switch and USB toy.




USB Can Be Power Only
USB is also a power source for many small devices. This Chromecast streamer gets its DC power from a USB port (conveniently nearby in this photo). See Chromecast. (Image courtesy of Google Inc.)






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


                           Transfer Rate
 Version (Year)               (Mbps)

 USB 1.1 (1998)             1.5 & 12
  (1.5 Mbps slow channel
  for keyboards, mice, etc.)

 USB 2.0 Hi-Speed (2001)       480

 USB 3.0 SuperSpeed (2008)    4800
  (see USB 3.0)

 USB 3.1 (2014)               9600
  (see USB 3.1)