ExtUSB

Universal Serial Bus (USB)

Certified USB logo
Type	Bus
Designer	Compaq, DEC, IBM, Intel, Microsoft, NEC and Nortel
Designed	January 1996; 21 years ago (1996-01)
Produced	Since May 1996
Superseded	Serial port, parallel port, game port, Apple Desktop Bus, PS/2 port, and MagSafe
Length	2–5 m (6 ft 7 in–16 ft 5 in) (by category)
Width	12 mm (type-A) 8.45 mm (type-B) 6.8 mm (mini/micro) 8.25 mm (type-C)
Height	4.5 mm (type-A) 7.26 mm (type-B) 10.44 mm (type-B SuperSpeed) 1.8–3 mm (mini/micro) 2.4 mm (type-C)
Hot pluggable	Yes
External	Yes
Cable	4 wires plus shield 9 wires plus shield (SuperSpeed)
Pins	4: 1 power, 2 data, 1 ground 5 (On-the-Go) 9 (SuperSpeed) 11 (Powered-B SuperSpeed) 24 (type-C)
Connector	Unique
Signal	5 V DC
Max. voltage	7000500000000000000♠5.00+0.25 −0.60 V 7000500000000000000♠5.00+0.25 −0.55 V (USB 3.0) 20.00 V (PD)
Max. current	0.5 A (USB 2.0) 0.9 A (USB 3.0) 5 A (BC 1.2) 3 A (type-C) Up to 5 A (PD)
Data signal	Packet data, defined by specifications
Width	1 bit
Bitrate	1.5, 12, 480, 5,000, 10,000 Mbit/s (depending on mode)
Max. devices	127
Protocol	Serial
The type-A plug (left) and type-B plug (right)
Pin 1		VBUS (+5 V)
Pin 2		Data−
Pin 3		Data+
Pin 4		Ground

USB, short for Universal Serial Bus, is an industry standard initially developed in the mid-1990s that defines the cables, connectors and used in a bus for connection, communication, and power supply between computers and electronic devices. It is currently developed by the USB Implementers Forum (USB IF).

USB was designed to standardize the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electric power. It has become commonplace on other devices, such as smartphones, PDAs and video game consoles. USB has effectively replaced a variety of earlier interfaces, such as parallel ports, as well as separate power chargers for portable devices.

In general, there are three basic formats of USB connectors: the default or standard format intended for desktop or portable equipment (for example, on USB flash drives), the mini intended for mobile equipment (now deprecated except the Mini-B, which is used on many cameras), and the thinner micro size, for low-profile mobile equipment (most modern mobile phones). Also, there are 5 modes of USB data transfer, in order of increasing bandwidth: Low Speed (from 1.0), Full Speed (from 1.0), High Speed (from 2.0), SuperSpeed (from 3.0), and SuperSpeed+ (from 3.1); modes have differing hardware and cabling requirements. USB devices have some choice of implemented modes, and USB version is not a reliable statement of implemented modes. Modes are identified by their names and icons, and the specifications suggests that plugs and receptacles be colour-coded (SuperSpeed is identified by blue).