USB connection
 
Certified USB logo
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| Type | Bus | ||
|---|---|---|---|
| Designer | Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel | ||
| Designed | January 1996 | ||
| 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| Superseded | Serial port, parallel port, game port, Apple Desktop Bus, PS/2 port, and MagSafe | ||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 |
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| Hot pluggable | Yes | ||
| External | Yes | ||
| Cable |
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| Pins |
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| Connector | Unique | ||
| Signal | 5 V DC | ||
| Max. voltage |
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| Max. current |
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| Data signal | Packet data, defined by specifications | ||
| Width | 1 bit | ||
| Bitrate | 1.5, 12, 480, 5,000, 10,000, 20,000 Mbit/s (depending on mode) | ||
| Max. devices | 127 | ||
| Protocol | Serial | ||
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| 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 that defines cables, connectors and for connection, communication, and power supply between computers and devices.
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 largely replaced a variety of earlier interfaces, such as serial ports and parallel ports, as well as separate power chargers for portable devices – and has become commonplace on a wide range of devices.
Created in the mid-1990s, it is currently developed by the USB Implementers Forum (USB IF).
The three sizes of USB connectors are the default or standard format intended for desktop or portable equipment, 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 such as mobile phones and tablets. In order of increasing bandwith there are 5 speeds for USB data transfer: Low Speed (from 1.0), Full Speed (from 1.0), High Speed (from 2.0), SuperSpeed (from 3.0), and SuperSpeed+ (from 3.1). The 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).
Unlike other data buses (e.g., Ethernet, HDMI), USB connections are directed, with both upstream and downstream ports emanating from a single host. This applies to electrical power, with only downstream facing ports providing power; this topology was chosen to easily prevent electrical overloads and damaged equipment. Thus, USB cables have different ends: A and B, with different physical connectors for each. Therefore, in general, each different format requires four different connectors: a plug and receptacle for each of the A and B ends. USB cables have the plugs, and the corresponding receptacles are on the computers or electronic devices. In common practice, the A end is usually the standard format, and the B side varies over standard, mini, and micro. The mini and micro formats also provide for USB On-The-Go with a hermaphroditic AB receptacle, which accepts either an A or a B plug. On-The-Go allows USB between peers without discarding the directed topology by choosing the host at connection time; it also allows one receptacle to perform double duty in space-constrained applications.
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Wikipedia