USB For the portable USB storage device, see USB flash from the point of designed insertion lifetime. The stan- drive. For other uses, see USB (disambiguation). dard and mini connectors were designed for less than daily connections, with a design lifetime of 1,500 in- [5] Universal Serial Bus (USB) is an industry standard de- sertion/removal cycles. (Improved mini-B connectors have reached 5,000-cycle lifetimes.) Micro connectors veloped in the mid-1990s that defines the cables, con- nectors and communications protocols used in a bus for were designed with frequent charging of portable devices in mind; not only is design lifetime of the connector im- connection, communication, and power supply between [5] computers and electronic devices.[2] proved to 10,000 cycles, but it was also redesigned to place the flexible contacts, which wear out sooner, on the USB was designed to standardize the connection of easily replaced cable, while the more durable rigid con- computer peripherals (including keyboards, pointing de- tacts are located in the micro-USB receptacles. Likewise, vices, digital cameras, printers, portable media players, the springy part of the retention mechanism (parts that disk drives and network adapters) to personal comput- provide required gripping force) were also moved into ers, both to communicate and to supply electric power. plugs on the cable side.[6] It has become commonplace on other devices, such as smartphones, PDAs and video game consoles.[3] USB has USB connections also come in five data transfer modes: effectively replaced a variety of earlier interfaces, such as Low Speed, Full Speed, High Speed, SuperSpeed, and serial and parallel ports, as well as separate power charg- SuperSpeed+. High Speed is only supported by specif- ers for portable devices. ically designed USB 2.0 High Speed interfaces (that is, USB 2.0 controllers without the High Speed designation do not support it), as well as by USB 3.0 and newer in- terfaces. SuperSpeed is supported only by USB 3.0 and 1 Overview newer interfaces, and requires a connector and cable with extra pins and wires, usually distinguishable by the blue In general, there are three basic kinds or sizes related inserts in connectors. to the USB connectors and types of established connec- tion: the older “standard” size, in its USB 1.1/2.0 and USB 3.0 variants (for example, on USB flash drives), the “mini” size (primarily for the B connector end, such as on 2 History many cameras), and the “micro” size, in its USB 1.1/2.0 and USB 3.0 variants (for example, on most modern cell- phones). Unlike other data cables (Ethernet, HDMI etc.), each end of a USB cable uses a different kind of connector; an A-type or a B-type. This kind of design was chosen to prevent electrical overloads and damaged equipment, as only the A-type socket provides power. There are cables with A-type connectors on both ends, but they should be used carefully.[4] Therefore, in general, each of the differ- ent “sizes” requires four different connectors; USB cables [7] have the A-type and B-type plugs, and the corresponding The basic USB trident logo receptacles are on the computer or electronic device. In common practice, the A-type connector is usually the full A group of seven companies began the development of size, and the B-type side can vary as needed. USB in 1994: Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel.[8] The goal was to make it fundamen- The mini and micro sizes also allow for a reversible AB- tally easier to connect external devices to PCs by replac- type receptacle, which can accept either an A-type or a ing the multitude of connectors at the back of PCs, ad- B-type plug. This scheme, known as "USB On-The-Go", dressing the usability issues of existing interfaces, and allows one receptacle to perform its double duty in space- simplifying software configuration of all devices con- constrained applications. nected to USB, as well as permitting greater data rates Counter-intuitively, the “micro” size is the most durable for external devices. A team including Ajay Bhatt worked 1 2 2 HISTORY 2.1.1 Version history overview 2.1.2 Prereleases The USB standard evolved through several versions be- fore its official release in 1996: • USB 0.8 – released in December 1994 • USB sign on the head of a standard-A plug, the most common USB 0.9 – released in April 1995 USB plug • USB 0.99 – released in August 1995 • USB 1.0 Release Candidate – released in November 1995 on the standard at Intel;[9][10] the first integrated circuits supporting USB were produced by Intel in 1995.[11] 2.1.3 USB 1.x The original USB 1.0 specification, which was introduced in January 1996, defined data transfer rates of 1.5 Mbit/s Released in January 1996, USB 1.0 specified data rates of [11] “Low Speed” and 12 Mbit/s “Full Speed”. The first 1.5 Mbit/s (Low Bandwidth or Low Speed) and 12 Mbit/s widely used version of USB was 1.1, which was released (Full Bandwidth or Full Speed). It did not allow for ex- in September 1998. The 12 Mbit/s data rate was in- tension cables or pass-through monitors, due to timing tended for higher-speed devices such as disk drives, and and power limitations. Few USB devices made it to the the lower 1.5 Mbit/s rate for low data rate devices such as market until USB 1.1 was released in August 1998, fixing [12] joysticks. problems identified in 1.0, mostly related to using hubs. The USB 2.0 specification was released in April 2000 and USB 1.1 was the earliest revision that was widely adopted. was ratified by the USB Implementers Forum (USB-IF) at the end of 2001. Hewlett-Packard, Intel, Lucent Tech- 2.1.4 USB 2.0 nologies (now Alcatel-Lucent), NEC and Philips jointly led the initiative to develop a higher data transfer rate, with the resulting specification achieving 480 Mbit/s, a 40-times increase over the original USB 1.1 specification. The USB 3.0 specification was published on 12 Novem- ber 2008. Its main goals were to increase the data transfer rate (up to 5 Gbit/s), decrease power consump- tion, increase power output, and be backward compat- ible with USB 2.0.[13] USB 3.0 includes a new, higher speed bus called SuperSpeed in parallel with the USB 2.0 bus.[14] For this reason, the new version is also called The Hi-Speed USB Logo SuperSpeed.[15] The first USB 3.0 equipped devices were presented in January 2010.[15][16] As of 2008, approximately six billion USB ports and in- terfaces were in the global marketplace, and about two billion were being sold each year.[17] In December 2014, USB-IF submitted USB 3.1, USB Power Delivery 2.0 and USB Type-C specifications to the IEC (TC 100 – Audio, video and multimedia systems and equipment) for inclusion in the international standard IEC 62680 “Universal Serial Bus interfaces for data and power”, which is currently based on USB 2.0.[18] A PCI USB 2.0 card for a computer motherboard USB 2.0 was released in April 2000, adding a higher max- 2.1 Version history imum signaling rate of 480 Mbit/s called High Speed, in addition to the USB 1.x Full Speed signaling rate of 2.1 Version history 3 12 Mbit/s. Due to bus access constraints, the effective This adds “sleep”, a new power state between en- throughput of the High Speed signaling rate is limited to abled and suspended states. Device in this state is 35 MB/s or 280 Mbit/s.[22][23] not required to reduce its power consumption. How- Further modifications to the USB specification have been ever, switching between enabled and sleep states is made via Engineering Change Notices (ECN). The most much faster than switching between enabled and important of these ECNs are included into the USB 2.0 suspended states, which allows devices to sleep specification package available from USB.org:[24] while idle. • Battery Charging Specification 1.2:[25] Released in • Mini-A and Mini-B Connector ECN: Released in Oc- December 2010. tober 2000. Several changes and increasing limits including al- Specifications for mini-A and B plug and recepta- lowing 1.5 A on charging ports for unconfigured de- cle. Also receptacle that accepts both plugs for On- vices, allowing High Speed communication while The-Go. These should not be confused with micro- having a current up to 1.5 A and allowing a maxi- B plug and receptacle. mum current of 5 A. • Pull-up/Pull-down Resistors ECN: Released in May 2002 2.1.5 USB 3.0 • Interface Associations ECN: Released in May 2003. New standard descriptor was added that allows asso- Main article: USB 3.0 ciating multiple interfaces with a single device func- USB 3.0 standard was released in November 2008, defin- tion. • Rounded Chamfer ECN: Released in October 2003. A recommended, backward compatible change to mini-B plugs that results in longer lasting connec- tors. • Unicode ECN: Released in February 2005. This ECN specifies that strings are encoded using UTF-16LE. USB 2.0 specified Unicode, but did not specify the encoding. • Inter-Chip USB Supplement: Released in March The SuperSpeed USB Logo 2006 • On-The-Go Supplement 1.3: Released in December ing a new SuperSpeed mode. A USB 3.0 port, usually col- 2006.