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Definition: USB

(1) See USB drive and USB port.

(2) (Universal Serial Bus) A hardware interface that can attach up to 127 peripheral devices to a computer, including keyboards, mice, printers, flash drives and external storage. USB is also used for charging phones, tablets and myriad portable devices (see USB power and USB charger).

The Peripheral Standard
Emerging in 1996 and governed by the USB Implementers Forum (see USB-IF), USB quickly replaced the serial and parallel ports on PCs and the Apple Desktop Bus on Macs (see serial port, parallel port and Apple Desktop Bus).

Names and Numbers
USB has two specifications. Letters and names define the type of port. Numbers designate the speed of the bus.

Hot Swappable Drives
USB devices can be plugged and unplugged while the computer is on. However, USB drives require a software "eject" beforehand to ensure that any pending data not yet written to the drive will be completed. See USB drive, USB device class, USB OTG, USB switch and USB toy.

USB Type C
Introduced in 2014, USB Type C was designed to replace all prior versions of USB. See USB Type C.

A 50,000x Increase in Speed
From 1996 to 2022, data transfer over USB increased more than 50,000 times, from 1.5 Mbps to 80 Gbps (see chart below).

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 logos show speed (5. 10, etc.) and replace the multiple obtuse designations for USB 3.x (see USB 3.2). DisplayPort requires USB-C cables (see USB Type C).

                       Data Rate  Lanes

 USB 4 Version 2.0      80 Gbps    2**
 USB 4 Version 1.0      40 Gbps    2**

 USB 3.2 Gen 2x2        20 Gbps    2**

 USB 3.2 Gen 1x2        10 Gbps    2**

 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 1x1         5 Gbps    1
 a.k.a. USB 3.1
 a.k.a. USB 3.0 Gen 1

 USB 2.0 High Speed    480 Mbps    1
 USB 2.0 Full Speed     12 Mbps    1
 USB 2.0 Slow Speed    1.5 Mbps    1

 ** 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.)

A Lotta Plugs and Sockets
From the mid-1990s to the mid-2010s, two Apple ports and a variety of USB ports came out. In 2014, USB Type C was introduced to eventually replace them all. See USB Type C.