Universal Serial Bus

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universal serial bus

[‚yü·nə‚vər·səl ‚sir·ē·əl ′bəs]
(computer science)
A serial interface that can transfer data at up to 480 million bits per second and connect up to 127 daisy-chained peripheral devices. Abbreviated USB.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Universal Serial Bus

(hardware, standard)
(USB) An external peripheral interface standard for communication between a computer and external peripherals over an inexpensive cable using biserial transmission.

USB is intended to replace existing serial ports, parallel ports, keyboard, and monitor connectors and be used with keyboards, mice, monitors, printers, and possibly some low-speed scanners and removable hard drives. For faster devices existing IDE, SCSI, or emerging FC-AL or FireWire interfaces can be used.

USB works at 12 Mbps with specific consideration for low cost peripherals. It supports up to 127 devices and both isochronous and asynchronous data transfers. Cables can be up to five metres long and it includes built-in power distribution for low power devices. It supports daisy chaining through a tiered star multidrop topology. A USB cable has a rectangular "Type A" plug at the computer end and a square "Type B" plug at the peripheral end.

Before March 1996 Intel started to integrate the necessary logic into PC chip sets and encourage other manufacturers to do likewise. It was widely available by 1997. Later versions of Windows 95 included support for it. It was standard on Macintosh computers in 1999.

The USB 2.0 specification was released in 2000 to allow USB to compete with Firewire etc. USB 2.0 is backward compatible with USB 1.1 but works at 480 Mbps.

usb.org.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

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.


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

 SuperSpeed+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 but is powered by USB (see Chromecast and USB power). (Image courtesy of Google Inc.)



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.)
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