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 (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] 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- 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 , 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 (, 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: , DEC, IBM, , , 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 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

USB 2.0 was released in April 2000, adding a higher - 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- 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. ored blue, is backward compatible with USB 2.0 devices USB On-The-Go makes it possible for two USB de- and cables. vices to communicate with each other without re- The USB 3.0 Promoter Group announced on 17 Novem- quiring a separate USB host. In practice, one of the ber 2008 that the specification of version 3.0 had been USB devices acts as a host for the other device. completed and had made the transition to the USB Im- plementers Forum (USB-IF), the managing body of USB • Battery Charging Specification 1.1: Released in specifications.[26] This move effectively opened the spec- March 2007 and updated on 15 April 2009. ification to hardware developers for implementation in Adds support for dedicated chargers (power supplies products. with USB connectors), host chargers (USB hosts that can act as chargers) and the No Dead Battery The new SuperSpeed bus provides a fourth transfer mode provision, which allows devices to temporarily draw with a of 5.0 Gbit/s, in addition to 100 mA current after they have been attached. If a the modes supported by earlier versions. The payload USB device is connected to dedicated charger, max- throughput is 4 Gbit/s (due to the overhead induced by imum current drawn by the device may be as high used 8b/10b encoding), and the specification considers as 1.8 A. (Note that this document is not distributed it reasonable to achieve around 3.2 Gbit/s (0.4 GB/s or with USB 2.0 specification package, only USB 3.0 400 MB/s), which should increase with future hardware and USB On-The-Go.) advances. Communication is full-duplex in SuperSpeed transfer mode; in the modes supported previously, by 1.x • Micro-USB Cables and Connectors Specification and 2.0, communication is half-duplex, with direction 1.01: Released in April 2007. controlled by the host.[27] • Link Power Management Addendum ECN: Released As with previous USB versions, USB 3.0 ports come in in July 2007. low-power and high-power variants, providing 150 mA 4 3 SYSTEM DESIGN

and 900 mA respectively, while simultaneously trans- power currents of 1.5 A and 3.0 A over the 5 V power mitting data at SuperSpeed rates.[28] Additionally, there bus in addition to baseline 900 mA; devices can either ne- is a Battery Charging Specification (Version 1.2 – De- gotiate increased USB current through the configuration cember 2010), which increases the power handling ca- line, or they can support the full Power Delivery specifica- pability to 1.5 A but does not allow concurrent data tion using both BMC-coded configuration line and legacy transmission.[25] The Battery Charging Specification re- BFSK-coded VBUS line. quires that the physical ports themselves be capable of Alternate Mode dedicates some of the physical wires in handling 5 A of current but limits the maximum current the type-C cable for direct device-to-host transmission of drawn to 1.5 A. alternate data protocols. The four high-speed lanes, two sideband pins, and— for dock, detachable device and per- 2.1.6 USB 3.1 manent cable applications only— two USB 2.0 pins and one configuration pin can be used for Alternate Mode A January 2013 press release from the USB group re- transmission. The modes are configured using VDMs vealed plans to update USB 3.0 to 10 Gbit/s.[29] The through the configuration channel. group ended up creating a new USB version, USB 3.1, which was released on 31 July 2013,[30] introducing a faster transfer mode called “SuperSpeed USB 10 Gbit/s”, 3 System design putting it on par with a single first-generation channel. The new mode’s logo features a "Superspeed+" caption (stylized as SUPERSPEED+). The USB 3.1 stan- The design architecture of USB is asymmetrical in its dard increases the data signaling rate to 10 Gbit/s in the topology, consisting of a host, a multitude of downstream USB 3.1 Gen2 mode, double that of USB 3.0 (referred USB ports, and multiple peripheral devices connected in to as USB 3.1 Gen1) and reduces line encoding over- a tiered-star topology. Additional USB hubs may be in- head to just 3% by changing the encoding scheme to cluded in the tiers, allowing branching into a tree struc- 128b/132b.[31] The first USB 3.1 implementation demon- ture with up to five tier levels. A USB host may imple- strated transfer speeds of 7.2 Gbit/s.[32] ment multiple host controllers and each host controller may provide one or more USB ports. Up to 127 de- The USB 3.1 standard is backward compatible with USB vices, including hub devices if present, may be connected 3.0 and USB 2.0. to a single host controller.[39][40] USB devices are linked in series through hubs. One hub—built into the host controller—is the root hub. 2.1.7 USB Type-C A physical USB device may consist of several logical sub- Main article: USB Type-C devices that are referred to as device functions. A sin- gle device may provide several functions, for example, Developed at roughly the same time as the USB 3.1 spec- a (video device function) with a built-in micro- ification, but distinctly from it, the USB type-C Speci- phone (audio device function). This kind of device is called a composite device. An alternative to this is com- fication 1.0 defines a new small reversible-plug connec- tor for USB devices.[33] The type-C plug connects to pound device, in which the host assigns each logical de- vice a distinctive address and all logical devices connect both hosts and devices, replacing various type-B and type-A connectors and cables with a standard meant to a built-in hub that connects to the physical USB cable. to be future-proof, similarly to Apple and USB device communication is based on pipes (logical Thunderbolt.[34][35][36] The 24-pin double-sided connec- channels). A pipe is a connection from the host con- tor provides four power/ground pairs, two differential troller to a logical entity, found on a device, and named an pairs for USB 2.0 data bus (though only one pair is imple- endpoint. Because pipes correspond 1-to-1 to endpoints, mented in a type-C cable), four pairs for high-speed data the terms are sometimes used interchangeably. A USB bus, two “sideband use” pins, and two configuration pins device could have up to 32 endpoints (16 IN, 16 OUT), for cable orientation detection, dedicated biphase mark though it’s rare to have so many. An endpoint is defined code (BMC) configuration data channel, and VCONN and numbered by the device during initialization (the pe- +5 V power for active cables.[37][38] Type-A and type-B riod after physical connection called “enumeration”) and adaptors/cables will be required for older devices in order so is relatively permanent, whereas a pipe may be opened to plug into type-C hosts; adaptors/cables with a type-C and closed. receptacle are not allowed. There are two types of pipe: stream and message. A mes- Full-featured USB Type-C cables are active, electroni- sage pipe is bi-directional and is used for control transfers. cally marked cables that contain a chip with an ID func- Message pipes are typically used for short, simple com- tion based on the configuration data channel and vendor- mands to the device, and a status response, used, for ex- defined messages (VDMs) from the USB Power Deliv- ample, by the bus control pipe number 0. A stream pipe is ery 2.0 specification. USB Type-C devices also support a uni-directional pipe connected to a uni-directional end- 5

Two USB 3.0 standard-A sockets (left) and two USB 2.0 sockets (right) on a computer’s front panel

When a USB device is first connected to a USB host, the USB device enumeration process is started. The enumer- ation starts by sending a reset signal to the USB device. USB endpoints actually reside on the connected device: the chan- The data rate of the USB device is determined during the nels to the host are referred to as pipes reset signaling. After reset, the USB device’s is read by the host and the device is assigned a unique 7- point that transfers data using an isochronous,[41] inter- bit address. If the device is supported by the host, the rupt, or bulk transfer: device drivers needed for communicating with the device are loaded and the device is set to a configured state. If • isochronous transfers: at some guaranteed data rate the USB host is restarted, the enumeration process is re- (often, but not necessarily, as fast as possible) peated for all connected devices. but with possible data loss (e.g., realtime audio or The host controller directs traffic flow to devices, so no video). USB device can transfer any data on the bus without an • interrupt transfers: devices that need guaranteed explicit request from the host controller. In USB 2.0, the quick responses (bounded ) (e.g., pointing host controller polls the bus for traffic, usually in a round- devices and keyboards). robin fashion. The throughput of each USB port is deter- mined by the slower speed of either the USB port or the • bulk transfers: large sporadic transfers using all re- USB device connected to the port. maining available bandwidth, but with no guarantees High-speed USB 2.0 hubs contain devices called transac- on bandwidth or latency (e.g., file transfers). tion translators that convert between high-speed USB 2.0 buses and full and low speed buses. When a high-speed An endpoint of a pipe is addressable with a tuple (de- USB 2.0 hub is plugged into a high-speed USB host or vice_address, endpoint_number) as specified in a TOKEN hub, it operates in high-speed mode. The USB hub then packet that the host sends when it wants to start a data uses either one transaction translator per hub to create a transfer session. If the direction of the data transfer is full/low-speed bus routed to all full and low speed devices from the host to the endpoint, an OUT packet (a special- on the hub, or uses one transaction translator per port to ization of a TOKEN packet) having the desired device create an isolated full/low-speed bus per port on the hub. address and endpoint number is sent by the host. If the di- rection of the data transfer is from the device to the host, Because there are two separate controllers in each USB the host sends an IN packet instead. If the destination 3.0 host, USB 3.0 devices transmit and receive at USB endpoint is a uni-directional endpoint whose manufac- 3.0 data rates regardless of USB 2.0 or earlier devices turer’s designated direction does not match the TOKEN connected to that host. Operating data rates for earlier packet (e.g., the manufacturer’s designated direction is IN devices are set in the legacy manner. while the TOKEN packet is an OUT packet), the TOKEN packet is ignored. Otherwise, it is accepted and the data transaction can start. A bi-directional endpoint, on the other hand, accepts both IN and OUT packets. 4 Device classes Endpoints are grouped into interfaces and each interface is associated with a single device function. An exception The functionality of USB devices is defined by class to this is endpoint zero, which is used for device con- codes, communicated to the USB host to affect the load- figuration and is not associated with any interface. A ing of suitable software driver modules for each con- single device function composed of independently con- nected device. This provides for adaptability and device trolled interfaces is called a composite device. A compos- independence of the host to support new devices from ite device only has a single device address because the different manufacturers. host only assigns a device address to a function. Device classes include:[42] 6 4 DEVICE CLASSES

4.1 USB / USB drive erals, including drives of various kinds. Firstly conceived and still used today for optical stor- age devices (CD-RW drives, DVD drives, etc.), sev- eral manufacturers offer external portable USB hard disk drives, or empty enclosures for disk drives. These of- fer performance comparable to internal drives, limited by the current number and types of attached USB de- vices, and by the upper limit of the USB interface (in practice about 30 MB/s for USB 2.0 and potentially 400 MB/s or more[46] for USB 3.0). These external drives typ- ically include a “translating device” that bridges between a drive’s interface to a USB interface port. Functionally, the drive appears to the user much like an internal drive. Other competing standards for external drive connectiv- A flash drive, a typical USB mass-storage device ity include eSATA, ExpressCard (now at version 2.0), FireWire (IEEE 1394), and most recently Thunderbolt. Another use for USB mass storage devices is the portable execution of software applications (such as web browsers and VoIP clients) with no need to install them on the host computer.[47][48]

4.2 Media Transfer Protocol

Media Transfer Protocol (MTP) was designed by Microsoft to give higher-level access to a device’s filesys- tem than USB mass storage, at the level of files rather than disk blocks. It also has optional DRM features. MTP was designed for use with portable media players, but it has since been adopted as the primary storage access proto- Circuit board from a USB 3.0 external 2.5-inch SATA HDD en- col of the Android from the version 4.1 closure Jelly Bean as well as Windows Phone 8 (Windows Phone 7 devices had used the Zune protocol which was an evo- See also: USB mass storage device class, lution of MTP). The primary reason for this is that MTP and External does not require exclusive access to the storage device the way UMS does, alleviating potential problems should an USB implements connections to storage devices using a Android program request the storage while it is attached set of standards called the USB mass storage device class to a computer. The main drawback is that MTP is not as (MSC or UMS). This was at first intended for traditional well supported outside of Windows operating systems. magnetic and optical drives and has been extended to sup- port flash drives. It has also been extended to support a wide variety of novel devices as many systems can be 4.3 Human interface devices controlled with the familiar metaphor of file manipula- tion within directories. The process of making a novel Main article: USB human interface device class device look like a familiar device is also known as exten- sion. The ability to boot a write-locked SD card with a Joysticks, keypads, tablets and other human-interface de- USB adapter is particularly advantageous for maintain- vices (HIDs) are also progressively migrating from MIDI, ing the integrity and non-corruptible, pristine state of the and PC connectors to USB. medium. USB mice and keyboards can usually be used with older Though most post-Summer 2004 computers can boot computers that have PS/2 connectors with the aid of a from USB mass storage devices, USB is not intended as a small USB-to-PS/2 adapter. For mice and keyboards with primary bus for a computer’s internal storage. Buses such dual-protocol support, an adaptor that contains no logic as Parallel ATA (PATA or IDE), Serial ATA (SATA), or circuitry may be used: the hardware in the USB keyboard SCSI fulfill that role in PC class computers. However, or mouse is designed to detect whether it is connected to a USB has one important advantage, in that it is possible USB or PS/2 port, and communicate using the appropri- to install and remove devices without rebooting the com- ate protocol. Converters also exist that connect PS/2 key- puter (hot-swapping), making it useful for mobile periph- boards and mice (usually one of each) to a USB port.[49] 5.1 Connector properties 7

These devices present two HID endpoints to the system and use a microcontroller to perform bidirectional data translation between the two standards.

4.4 Device Firmware Upgrade

Device Firmware Upgrade (DFU) is a vendor- and device- independent mechanism for upgrading the firmware of USB devices with improved versions provided by their manufacturers, offering (for example) a way for firmware bugfixes to be deployed. During the firmware upgrade operation, USB devices change their operating mode ef- fectively becoming a PROM programmer. Any class of USB device can implement this capability by following the official DFU specifications.[45][50][51] In addition to its intended legitimate purposes, DFU can also be exploited by uploading maliciously crafted firmwares that cause USB devices to spoof various other device types; one such exploiting approach is known as USB extension cable BadUSB.[52] required USB must be embossed on the “topside” of the USB plug, which "...provides easy user recognition 5 Connectors and plugs and facilitates alignment during the mating process.” The specification also shows that the “recommended” “Manu- 5.1 Connector properties facturer’s logo” (“engraved” on the diagram but not spec- ified in the text) is on the opposite side of the USB icon. The specification further states, “The USB Icon is also lo- cated adjacent to each receptacle. Receptacles should be oriented to allow the icon on the plug to be visible dur- ing the mating process.” However, the specification does not consider the height of the device compared to the eye level height of the user, so the side of the cable that is “vis- ible” when mated to a computer on a desk can depend on whether the user is standing or kneeling.[53] While it would have been better for usability if the cable could be plugged in with either side up, the original design left this out to make manufacturing as inexpensive as pos- sible. Ajay Bhatt, who was involved in the original USB design team, is working on a new design to make the cable insertable either side up.[55] The new reversible type-C plug is an addition to the USB 3.1 specification; it is much Standard type A plug and receptacle smaller than the current USB 3.0 micro-B connector[56] The connectors the USB committee specifies support a Only moderate force is needed to insert or remove a USB number of USB’s underlying goals, and reflect lessons cable. USB cables and small USB devices are held in learned from the many connectors the computer industry place by the gripping force from the receptacle (without has used. The connector mounted on the host or device need of the screws, clips, or thumb-turns other connec- is called the receptacle, and the connector attached to the tors have required). cable is called the plug.[53] The official USB specification documents also periodically define the term male to rep- resent the plug, and female to represent the receptacle.[54] 5.1.2 Power-use topology

The standard connectors were deliberately intended to 5.1.1 Usability and orientation enforce the directed topology of a USB network: type A connectors on host devices that supply power and type B By design, it is difficult to insert a USB plug into its re- connectors on target devices that draw power. This is in- ceptacle incorrectly. The USB specification states that the tended to prevent users from accidentally connecting two 8 5 CONNECTORS AND PLUGS

USB power supplies to each other, which could lead to of a connecting device in the area around its plug. This short circuits and dangerously high currents, circuit fail- was done to prevent a device from blocking adjacent ports ures, or even fire. USB does not support cyclic networks due to the size of the cable strain relief mechanism (usu- and the standard connectors from incompatible USB de- ally molding integral with the cable outer insulation) at vices are themselves incompatible.[4] the connector. Compliant devices must either fit within However, some of this directed topology is lost with the the size restrictions or support a compliant extension ca- advent of multi-purpose USB connections (such as USB ble that does. On-The-Go in smartphones, and USB-powered Wi-Fi In general, USB cables have only plugs on their ends, routers), which require A-to-A, B-to-B, and sometimes while hosts and devices have only receptacles. Hosts al- Y/splitter cables. See the USB On-The-Go connectors most universally have type-A receptacles, while devices section below, for a more detailed summary description. have one or another type-B variety. Type-A plugs mate only with type-A receptacles, and the same applies to their type-B counterparts; they are deliberately physically 5.1.3 Durability incompatible. However, an extension to the USB stan- dard specification called USB On-The-Go (OTG) allows The standard connectors were designed to be robust. Be- a single port to act as either a host or a device, what is cause USB is hot-pluggable, the connectors would be selectable by the end of the cable that plugs into the re- used more frequently, and perhaps with less care, than ceptacle on the OTG-enabled unit. Even after the cable other connectors. Many previous connector designs were is hooked up and the units are communicating, the two fragile, specifying embedded component pins or other units may “swap” ends under program control. This ca- delicate parts that were vulnerable to bending or break- pability is meant for units such as PDAs in which the USB ing. The electrical contacts in a USB connector are pro- link might connect to a PC’s host port as a device in one tected by an adjacent plastic tongue, and the entire con- instance, yet connect as a host itself to a keyboard and necting assembly is usually protected by an enclosing mouse device in another instance. metal sheath.[57] The connector construction always ensures that the ex- ternal sheath on the plug makes contact with its coun- USB 3.0 connectors See also: USB 3.0 § Backward terpart in the receptacle before any of the four connec- compatibility tors within make electrical contact. The external metallic sheath is typically connected to system ground, thus dis- Type-A plugs and receptacles from both USB 3.0 and sipating damaging static charges. This enclosure design USB 2.0 are designed to interoperate. Type-B plugs and also provides a degree of protection from electromagnetic receptacles in USB 3.0 are somewhat larger than those in interference to the USB signal while it travels through the USB 2.0; thus, USB 2.0 type-B plugs can fit into USB 3.0 mated connector pair (the only location when the other- type-B receptacles, while the opposite is not possible. wise twisted data pair travels in parallel). In addition, because of the required sizes of the power and common connections, they are made after the system ground but 5.2 Connector types before the data connections. This type of staged make- break timing allows for electrically safe hot-swapping.[57] The newer micro-USB receptacles are designed for up to 10,000 cycles of insertion and removal between the re- ceptacle and plug, compared to 1,500 for the standard USB and 5,000 for the mini-USB receptacle. To accom- plish this, a locking device was added and the leaf-spring was moved from the jack to the plug, so that the most- stressed part is on the cable side of the connection. This Types of USB connector left to right (ruler in centimeters): change was made so that the connector on the less expen- micro-B plug, UC-E6 proprietary (non-USB) plug, mini-B sive cable would bear the most wear instead of the more plug, standard-A receptacle (upside down), standard-A plug, expensive micro-USB device.[6][57] standard-B plug There are several types of USB connector, includ- 5.1.4 Compatibility ing some that have been added while the specification progressed. The original USB specification detailed The USB standard specifies relatively loose tolerances for standard-A and standard-B plugs and receptacles; the B compliant USB connectors to minimize physical incom- connector was necessary so that cabling could be plug patibilities in connectors from different vendors. To ad- ended at both ends and still prevent users from connecting dress a weakness present in some other connector stan- one computer receptacle to another. The first engineering dards, the USB specification also defines limits to the size change notice to the USB 2.0 specification added mini-B 5.2 Connector types 9 plugs and receptacles. 5.2.2 Mini and micro connectors The data pins in the standard-A plug are actually recessed in the plug compared to the outside power pins. This per- mits the power pins to connect first, preventing data errors by allowing the device to power up first and then establish the data connection. Also, some devices operate in dif- ferent modes depending on whether the data connection is made. To reliably enable a charge-only feature, modern USB ac- cessory peripherals now include charging cables that pro- vide power connections to the host port but no data con- nections, and both home and vehicle charging docks are available that supply power from a converter device and do not include a host device and data pins, allowing any capable USB device to charge or operate from a standard USB cable.

5.2.1 Standard connectors

Micro-A USB

Pin configuration of the standard-A and standard-B USB con- nectors, viewed from the mating end of plugs

The USB 2.0 standard-A type of USB plug is a flattened rectangle that inserts into a “downstream-port” recepta- cle on the USB host, or a hub, and carries both power and data. This plug is frequently seen on cables that are per- manently attached to a device, such as one connecting a keyboard or mouse to the computer via USB connection. USB connections eventually wear out as the connection loosens through repeated plugging and unplugging. The Micro-B USB lifetime of a USB-A male connector is approximately [58] 1,500 connect/disconnect cycles. Various connectors have been used for smaller devices A standard-B plug— which has a square shape with such as digital cameras, smartphones, and tablet com- beveled exterior corners— typically plugs into an “up- puters. These include the now-deprecated[61] (i.e. de- stream receptacle” on a device that uses a removable ca- certified but standardized) mini-A and mini-AB connec- ble, e.g., a . On some devices, the type-B re- tors; mini-B connectors are still supported, but are not ceptacle has no data connections, being used solely for OTG-compliant (On The Go, used in mobile devices).[62] accepting power from the upstream device. This two- The mini-B USB connector was standard for transferring connector-type scheme (A/B) prevents a user from ac- data to and from the early smartphones and PDAs. Both cidentally creating an electrical loop.[59] mini-A and mini-B plugs are approximately 3 by 7 mm; the mini-A connector and the mini-AB receptacle con- Maximum allowed size of the overmold boot (which is [63] part of the connector used for its handling) is 16 by 8 nector were deprecated on 23 May 2007. mm for the standard-A plug type, while for the type B it The micro-USB connector was announced by the USB-IF is 11.5 by 10.5 mm.[60] on 4 January 2007.[5][64] Micro-USB plugs have a similar 10 5 CONNECTORS AND PLUGS

standing (MoU).[71][72] Apple, one of the original MoU signers, makes micro-USB adapters available – as permit- ted in the Common EPS MoU – for its iPhones equipped with Apple’s proprietary 30 pin dock connector or (later) "Lightning" connector.[73][74]

5.2.3 USB On-The-Go connectors

Main article: USB On-The-Go

All current USB On-The-Go (OTG) devices are required USB mini-A (left) and USB mini-B (right) plugs to have one, and only one, USB connector: a micro-AB receptacle. Non-OTG compliant devices are not allowed to use the micro-AB receptacle, due to power supply width to mini-USB, but approximately half the thickness, shorting hazards on the VBUS line. The micro-AB recep- enabling their integration into thinner portable devices. tacle is capable of accepting both micro-A and micro-B The micro-A connector is 6.85 by 1.8 mm with a max- plugs, attached to any of the legal cables and adapters as imum overmold boot size of 11.7 by 8.5 mm, while the defined in revision 1.01 of the micro-USB specification. micro-B connector is 6.85 by 1.8 mm with a maximum Prior to the development of micro-USB, USB On-The- overmold size of 10.6 by 8.5 mm.[65] Go devices were required to use mini-AB receptacles to The thinner micro connectors are intended to replace the perform the equivalent job. mini connectors in new devices including smartphones, To enable type-AB receptacles to distinguish which end personal digital assistants, and cameras.[66] While some of a cable is plugged in, mini and micro plugs have of the devices and cables still use the older mini variant, an “ID” pin in addition to the four contacts found in the newer micro connectors are widely adopted, and as of standard-size USB connectors. This ID pin is connected December 2010 they are the most widely used. to GND in type-A plugs, and left unconnected in type-B The micro plug design is rated for at least 10,000 connect- plugs. Typically, a pull-up resistor in the device is used disconnect cycles, which is more than the mini plug to detect the presence or absence of an ID connection. design.[5][67] The micro connector is also designed to The OTG device with the A-plug inserted is called the A- reduce the mechanical wear on the device; instead the device and is responsible for powering the USB interface easier-to-replace cable is designed to bear the mechani- when required and by default assumes the role of host. cal wear of connection and disconnection. The Universal The OTG device with the B-plug inserted is called the B- Serial Bus Micro-USB Cables and Connectors Specification device and by default assumes the role of peripheral. An details the mechanical characteristics of micro-A plugs, OTG device with no plug inserted defaults to acting as a micro-AB receptacles (which accept both micro-A and B-device. If an application on the B-device requires the micro-B plugs), and micro-B plugs and receptacles,[67] role of host, then the Host Negotiation Protocol (HNP) is along with a standard-A receptacle to micro-A plug used to temporarily transfer the host role to the B-device. adapter. OTG devices attached either to a peripheral-only B- The cellular phone carrier group Open Mobile Termi- device or a standard/embedded host have their role fixed nal Platform (OMTP) in 2007 endorsed micro-USB by the cable, since in these scenarios it is only possible to as the standard connector for data and power on mo- attach the cable one way. bile devices[68] In addition, on 22 October 2009 the International Union (ITU) has also announced that it had embraced micro-USB as the Uni- versal Charging Solution its “energy-efficient one-charger- 5.2.4 Host and device interface receptacles fits-all new mobile phone solution”, and added: “Based on the Micro-USB interface, UCS chargers also include a 4- A pre-USB 3.0 connector (receptacles and plugs) mating star or higher efficiency rating— up to three times more [69] matrix is displayed below. As a note, the assignment of energy-efficient than an unrated charger.” functions (VCC, D+, D−, GND and ID) to pin numbers The European Standardisation Bodies CEN, CENELEC marked below is mostly consistent, with the exception of and ETSI (independent of the OMTP/GSMA proposal) mini and micro connectors. When compared to standard- defined a common External Power Supply (EPS) for use sized connectors (type-A and type-B), mini and micro with smartphones sold in the EU based on micro-USB.[70] connectors have their GND connections moved from pin 14 of the world’s largest mobile phone manufacturers #4 to pin #5, while their pin #4 serves as an ID pin for the signed the EU’s common EPS Memorandum of Under- On-The-Go host/client identification.[75] 5.3 Pinouts 11

5.2.5 Cable plugs (USB 1.x/2.0) 5.3 Pinouts

USB cables exist with various combinations of plugs on See also: USB 3.0 § Pinouts each end of the cable, as displayed below. Notes from the section above apply here as well. USB is a serial bus, using four shielded wires for the USB 2.0 variant: two for power (VBUS and GND), and two Non-standard Existing for specific proprietary pur- for differential data signals (labelled as D+ and D− in poses, and in most cases not inter-operable with pinouts). Non-Return-to-Zero Inverted (NRZI) encod- USB-IF compliant equipment. However, there do ing scheme is used for transferring data, with a sync field exist compliant A-to-A cables with a circuit in the to synchronise the host and receiver clocks. D+ and D− middle that behaves as a pair of devices, such as the signals are transmitted on a twisted pair, providing half- Easy Transfer Cable. duplex data transfers for USB 2.0. In addition to the above cable assemblies comprising USB 3.0 provides two additional twisted pairs (four wires, two plugs, an “adapter” cable with a micro-A plug SSTx+, SSTx−, SSRx+ and SSRx−), providing full- and a standard-A receptacle is compliant with USB duplex data transfers at “super-speed”, which makes it specifications.[65] Other combinations of connectors similar to Serial ATA or single-lane PCI Express. are not compliant.

Deprecated Some older devices and cables with mini- 1 2 A connectors have been certified by USB-IF. The mini-A connector is obsolete: no new mini-A con- nectors and neither mini-A nor mini-AB receptacles will be certified.[61] 4 23 1 4 3 Type A Type B

5.2.6 Cable plugs (USB 3.0) 5 4 123 5 4 123

Mini-A Mini-B

12345 12345 Micro-A Micro-B

Standard, mini, and micro USB plugs (not to scale). The white areas in these drawings represent hollow spaces. As the plugs are shown here, the USB logo (with optional letter A or B) is on the top of the overmold boot in all cases. Pin numbering looking into receptacles is mirrored from plugs, such that pin 1 on plug connects to pin 1 on the receptacle.[65]

USB 3.0 micro-B plug 5.3.1 Proprietary connectors and formats

See also: USB 3.0 § Connectors Manufacturers of personal electronic devices might not include a USB standard connector on their product for [76] USB 3.0 introduced new standard and micro-sized type technical or marketing reasons. Some manufacturers A and type B plugs and receptacles. The 3.0 receptacles provide proprietary cables that permit their devices to are backward-compatible with the corresponding pre-3.0 physically connect to a USB standard port. Full function- plugs. See the micro-B cable plug photo on the right. The ality of proprietary ports and cables with USB standard micro-B 3.0 plug effectively consists of a standard USB ports is not assured; for example, some devices only use 1.x/2.0 micro-B cable plug, with an additional five-pin the USB connection for battery charging and do not im- [77] plug “stacked” to the side of it. In this way, USB 3.0 plement any data transfer functions. micro-A host connectors can achieve backward compat- ibility with the USB 1.x/2.0 micro-B cable plugs. • HTC ExtMicro USB port and connector 12 7 POWER

USB 2.0 provides for a maximum cable length of 5 me- ters for devices running at Hi Speed (480 Mbit/s). The primary reason for this limit is the maximum allowed round-trip of about 1.5 μs. If USB host commands are unanswered by the USB device within the allowed time, the host considers the command lost. When adding USB device response time, delays from the maximum Micro-B USB 3.0 plug number of hubs added to the delays from connecting ca- bles, the maximum acceptable delay per cable amounts 1. Power (VBUS, 5 V) to 26 ns.[82] The USB 2.0 specification requires that ca- 2. USB 2.0 data− (D−) ble delay be less than 5.2 ns per meter (192 000 km/s, which is close to the maximum achievable transmission 3. USB 2.0 data+ (D+) speed for standard copper wire). 4. ID (USB OTG) The USB 3.0 standard does not directly specify a max- 5. GND imum cable length, requiring only that all cables meet 6. USB 3.0 transmit− (SSTx−) an electrical specification: for copper cabling with AWG 7. USB 3.0 transmit+ (SSTx+) 26 wires the maximum practical length is 3 meters (9.8 [83] 8. GND ft). 9. USB 3.0 receive− (SSRx−) 10. USB 3.0 receive+ (SSRx+) 7 Power

• Nokia Pop-Port connector

• An Apple Lightning-to-USB Cable

5.4 Colors

USB ports and connectors are often color-coded to distin- guish their different functions and USB versions. These colors are not part of the USB specification and can vary between manufacturers; for example, USB 3.0 specifica- tion mandates appropriate color-coding while it only rec- ommends blue inserts for standard-A USB 3.0 connectors and plugs.[78]

Y-shaped USB 3.0 cable; with such a cable, a device can draw power from two USB ports simultaneously 6 Cabling The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices. The Data + Data − specification provides for no more than 5.25 V and no less than 4.75 V (5 V ± 5%) between the positive and A USB twisted pair, where the “Data +" and “Data −" conductors negative bus power lines (VBUS voltage). For USB 3.0, are twisted together in a double helix. The wires are enclosed in the voltage supplied by low-powered hub ports is 4.45– a further layer of shielding. 5.25 V.[84] A unit load is defined as 100 mA in USB 1.x and 2.0, The data cables for USB 1.x and USB 2.x use a twisted and 150 mA in USB 3.0. A device may draw a maxi- pair to reduce noise and crosstalk. USB 3.0 cables contain mum of five unit loads (500 mA) from a port in USB 1.x twice as many wires as USB 2.x to support SuperSpeed [79] and 2.0, or six unit loads (900 mA) in USB 3.0. There data transmission, and are thus larger in diameter. are two types of device: low-power and high-power. A The USB 1.1 standard specifies that a standard cable can low-power device (such as a USB HID) draws at most have a maximum length of 5 meters with devices oper- one-unit load, with minimum operating voltage of 4.4 V ating at Full Speed (12 Mbit/s), and a maximum length in USB 2.0, and 4 V in USB 3.0. A high-power device of 3 meters with devices operating at Low Speed (1.5 draws, at most, the maximum number of unit loads the Mbit/s).[80][81] standard permits. Every device functions initially as low- 7.1 Charging ports 13

power (including high-power functions during their low- power enumeration phases), but may request high-power, and get it if available on the providing bus.[85][86][87][88] Some devices, such as high-speed external disk drives, require more than 500 mA of current[89] and therefore may have power issues if powered from just one USB 2.0 port: erratic function, failure to function, or over- loading/damaging the port. Such devices may come with an external power source or a Y-shaped cable that has two USB connectors (one for power and data, the other This USB power meter additionally provides a charge readout (in for power only) to plug into a computer. With such a mAh) and data logging cable, a device can draw power from two USB ports simultaneously.[90] However, USB compliance specifica- tion states that “use of a 'Y' cable (a cable with two A- plugs) is prohibited on any USB peripheral”, meaning that tween 500 mA and 1.5 A without the digital negotiation. “if a USB peripheral requires more power than allowed by A charging port supplies up to 500 mA at 5 V, up to the the USB specification to which it is designed, then it must rated current at 3.6 V or more, and drops its output volt- be self-powered.”[91] age if the portable device attempts to draw more than the rated current. The charger port may shut down if the load A bus-powered hub initializes itself at one-unit load and [92] transitions to maximum unit loads after it completes hub is too high. configuration. Any device connected to the hub draws Two types of charging port exist: the charging down- one-unit load regardless of the current draw of devices stream port (CDP), supporting data transfers as well, and connected to other ports of the hub (i.e., one device con- the dedicated charging port (DCP), without data support. nected on a four-port hub draws only one-unit load de- A portable device can recognize the type of USB port; on spite the fact that more unit loads are being supplied to a dedicated charging port, the D+ and D− pins are shorted the hub).[85] with a resistance not exceeding 200 ohms, while charging downstream ports provide additional detection logic so A self-powered hub supplies maximum supported unit [92] loads to any device connected to it. In addition, the VBUS their presence can be determined by attached devices. presents one-unit load upstream for communication if With charging downstream ports, current passing through parts of the Hub are powered down.[85] the thin ground wire may interfere with high-speed data signals; therefore, current draw may not exceed 900 mA during high-speed data transfer. A dedicated charge port 7.1 Charging ports may have a rated current between 500 and 1,500 mA. For all charging ports, there is maximum current of 5 A, as long as the connector can handle the current (standard USB 2.0 A-connectors are rated at 1.5 A).[92] Before the battery charging specification was defined, there was no standardized way for the portable device to inquire how much current was available. For example, Apple’s iPod and iPhone chargers indicate the available current by voltages on the D− and D+ lines. When D+ = D− = 2.0 V, the device may pull up to 500 mA. When D+ = 2.0 V and D− = 2.8 V, the device may pull up to 1 A of current.[93] When D+ = 2.8 V and D− = 2.0 V, the device may pull up to 2 A of current.[94] Dedicated charging ports can be found on USB power adapters that convert utility power or another power source (e.g., a car’s electrical system) to run attached de- A small gadget that provides voltage and current readouts for vices and battery packs. On a host (such as a com- devices charged over USB puter) with both standard and charging USB ports, the [92] The USB Battery Charging Specification Revision 1.1 (re- charging ports should be labeled as such. leased in 2007) defines a new type of USB port, called the To support simultaneous charge and data communica- charging port. Contrary to the standard downstream port, tion, even if the communication port does not support for which current draw by a connected portable device charging a demanding device, so-called accessory charg- can exceed 100 mA only after digital negotiation with ing adapters (ACA) are introduced. By using an acces- the host or hub, a charging port can supply currents be- sory charging adapter, a device providing a single USB 14 7 POWER

port can be attached to both a charger, and another USB device at the same time.[92] The USB Battery Charging Specification Revision 1.2 (re- leased in 2010) makes clear that there are safety lim- its to the rated current at 5 A coming from USB 2.0. On the other hand, several changes are made and lim- its are increasing including allowing 1.5 A on charging A yellow USB port denoting sleep-and-charge downstream ports for unconfigured devices, allowing high speed communication while having a current up to 1.5 A, and allowing a maximum current of 5 A. Also, revision 7.3 Sleep-and-charge ports 1.2 removes support for USB ports type detection via re- sistive detection mechanisms.[25] Sleep-and-charge USB ports can be used to charge elec- tronic devices even when the computer is switched off. Normally, when a computer is powered off the USB ports are powered down, preventing phones and other devices from charging. Sleep-and-charge USB ports remain pow- ered even when the computer is off. On , charging 7.2 USB Power Delivery devices from the USB port when it is not being powered from AC drains the laptop battery faster; most laptops have a facility to stop charging if their own battery charge In July 2012, the USB Promoters Group announced the level gets too low.[100] finalization of the USB Power Delivery (“PD”) speci- fication, an extension that specifies using certified “PD Sleep-and-charge USB ports may be found colored dif- aware” USB cables with standard USB type A and B con- ferently than regular ports, mostly red or yellow, though nectors to deliver increased power (more than 7.5 W) to that is not always the case. devices with larger power demand. Devices can request On and laptops, the port is marked with the higher currents and supply voltages from compliant hosts standard USB symbol with an added lightning bolt icon – up to 2 A at 5 V (for a power consumption of up to 10 on the right side. Dell calls this feature “PowerShare”,[101] W), and optionally up to 3 A or 5 A at either 12 V (36 while Toshiba calls it “USB Sleep-and-Charge”.[102] On W or 60 W) or 20 V (60 W or 100 W).[95] In all cases, Acer Inc. and Packard Bell laptops, sleep-and-charge both host-to-device and device-to-host configurations are USB ports are marked with a non-standard symbol (the supported.[96] letters “USB” over a drawing of a battery); the feature [103] The intent is to permit uniformly charging laptops, is simply called “Power-off USB”. On some laptops tablets, USB-powered disks and similarly higher power such as Dell and Apple MacBook models, it is possible consumer electronics, as a natural extension of existing to plug a device in, close the laptop (putting it into sleep European and Chinese mobile telephone charging stan- mode) and have the device continue to charge. dards. This may also affect the way electric power used for small devices is transmitted and used in both residen- tial and public buildings.[55][97] 7.4 Mobile device charger standards The Power Delivery specification defines six fixed power 7.4.1 In China profiles for the power sources. PD-aware devices imple- ment a flexible power management scheme by interfacing As of 14 June 2007, all new mobile phones applying for with the power source through a bidirectional data chan- a license in China are required to use a USB port as a nel and requesting a certain level of electrical power, vari- power port for battery charging.[104][105] This was the first able up to 5 A and 20 V depending on supported profile. standard to use the convention of shorting D+ and D-.[106] The power configuration protocol uses a 24 MHz BFSK- coded transmission channel on the VBUS line. 7.4.2 OMTP/GSMA Universal Charging Solution The USB Power Delivery revision 2.0 specification has been released as part of the USB 3.1 suite.[98] It covers the type-C cable and connector with four power/ground pairs In September 2007, the Open Mobile Terminal Platform and a separate configuration channel, which now hosts a group (a forum of mobile network operators and manu- DC coupled low-frequency BMC-coded data channel that facturers such as Nokia, Samsung, Motorola, Eric- reduces the possibilities for RF interference.[99] Power sson and LG) announced that its members had agreed on micro-USB as the future common connector for mobile Delivery protocols have been updated to facilitate type-C [107][108] features such as cable ID function, Alternate Mode nego- devices. tiation, increased VBUS currents, and VCONN-powered The GSM Association (GSMA) followed suit on 17 accessories. February 2009,[109][109][110][111][112] and on 22 April 7.5 Non-standard devices 15

USB-powered mini fans

The micro-USB interface is commonly found on chargers for mobile phones

2009, this was further endorsed by the CTIA – The Wire- less Association,[113] with the International Telecommu- nication Union (ITU) announcing on 22 October 2009 that it had also embraced the Universal Charging Solu- tion as its “energy-efficient one-charger-fits-all new mo- bile phone solution”, and added: “Based on the Micro- USB interface, UCS chargers will also include a 4-star or higher efficiency rating—up to three times more energy- efficient than an unrated charger.”[114]

7.4.3 EU Power Supply Standard USB vacuum cleaner novelty device Main article: Common External Power Supply vice. Some USB ports and external hubs can, in practice, In June 2009, many of the world’s largest mobile supply more power to USB devices than required by the phone manufacturers signed an EC-sponsored Memoran- specification but a standard-compliant device may not de- dum of Understanding (MoU), agreeing to make most pend on this. data-enabled mobile phones marketed in the European Union compatible with a common External Power Sup- In addition to limiting the total average power used by ply (EPS). The EU’s common EPS specification (EN the device, the USB specification limits the inrush current 62684:2010) references the USB Battery Charging stan- (i.e., that used to charge decoupling and filter capacitors) dard and is similar to the GSMA/OMTP and Chi- when the device is first connected. Otherwise, connect- nese charging solutions.[115][116] In January 2011, the ing a device could cause problems with the host’s internal International Electrotechnical Commission (IEC) re- power. USB devices are also required to automatically leased its version of the (EU’s) common EPS standard enter ultra low-power suspend mode when the USB host as IEC 62684:2011.[117] is suspended. Nevertheless, many USB host interfaces do not cut off the power supply to USB devices when they are suspended.[118] 7.5 Non-standard devices Some non-standard USB devices use the 5 V power sup- ply without participating in a proper USB network, which Some USB devices require more power than is permitted negotiates power draw with the host interface. These are by the specifications for a single port. This is common usually called USB decorations. Examples include USB- for external hard and drives, and generally powered keyboard lights, fans, mug coolers and heaters, for devices with motors or lamps. Such devices can use battery chargers, miniature vacuum cleaners, and even an external power supply, which is allowed by the stan- miniature lava lamps. In most cases, these items contain dard, or use a dual-input USB cable, one input of which no digital circuitry, and thus are not standard compliant is used for power and data transfer, the other solely for USB devices. This may cause problems with some com- power, which makes the device a non-standard USB de- puters, such as drawing too much current and damaging 16 8 SIGNALING

circuitry. Prior to the Battery Charging Specification, the USB signals are transmitted using differential signaling on USB specification required that devices connect in a low- a twisted-pair data cable with 90 Ω ±15% characteristic power mode (100 mA maximum) and communicate their impedance.[123] current requirements to the host, which then permits the device to switch into high-power mode. • Low- and full-speed modes (USB 1.x) use a single data pair, labeled D+ and D−, in half-duplex. Trans- Some devices, when plugged into charging ports, draw mitted signal levels are 0.0 to 0.3 V for logical low, even more power (10 watts or 2.1 amperes) than the Bat- and 2.8 to 3.6 V for logical high level. The signal tery Charging Specification allows. The iPad and MiFi lines are not terminated. 2200 are two such devices.[119] Barnes & Noble NOOK Color devices also require a special charger that runs at • High-speed mode (USB 2.0) uses the same wire 1.9 amperes.[120] pair, but with different electrical conventions. Lower signal voltages of −10 to 10 mV for low and 360 to 440 mV for logical high level, and 7.6 PoweredUSB termination of 45 Ω to ground, or 90 Ω differential to match the data cable impedance. Main article: PoweredUSB • SuperSpeed (USB 3.0) adds two additional pairs of shielded twisted wire (and new, mostly compatible PoweredUSB is a proprietary extension that adds four ad- expanded connectors), dedicated to full-duplex Su- ditional pins supplying up to 6 A at 5 V, 12 V, or 24 V. It perSpeed operation. The half-duplex lines are still is commonly used in systems to power pe- used for configuration. ripherals such as barcode readers, credit card terminals, and printers. A USB connection is always between a host or hub at the “A” connector end, and a device or hub’s “upstream” port at the other end. Originally, this was a “B” connector, preventing erroneous loop connections, but additional up- 8 Signaling stream connectors were specified, and some cable ven- dors designed and sold cables that permitted erroneous USB allows the following signaling rates (the terms speed connections (and potential damage to circuitry). USB in- and bandwidth are used interchangeably, while “high-" is terconnections are not as fool-proof or as simple as orig- alternatively written as “hi-"): inally intended. The host includes 15 kΩ pull-down resistors on each data • A low-speed (USB 1.0) rate of 1.5 Mbit/s is defined line. When no device is connected, this pulls both data by USB 1.0. It is very similar to full-bandwidth op- lines low into the so-called “single-ended zero” state (SE0 eration except each bit takes 8 times as long to trans- in the USB documentation), and indicates a reset or dis- mit. It is intended primarily to save cost in low- connected connection. bandwidth human interface devices (HID) such as A USB device pulls one of the data lines high with a 1.5 keyboards, mice, and joysticks. kΩ resistor. This overpowers one of the pull-down resis- tors in the host and leaves the data lines in an idle state • The full-speed (USB 1.1) rate of 12 Mbit/s is the called “J”. For USB 1.x, the choice of data line indicates basic USB data rate defined by USB 1.0. All USB of what signal rates the device is capable; full-bandwidth hubs can operate at this speed. devices pull D+ high, while low-bandwidth devices pull D− high. The “k” state is just the opposite polarity to the • A high-speed (USB 2.0) rate of 480 Mbit/s was in- “j” state. troduced in 2001. All hi-speed devices are capable of falling back to full-bandwidth operation if neces- USB data is transmitted by toggling the data lines between sary; i.e., they are backward compatible with USB the J state and the opposite K state. USB encodes data 1.1. Connectors are identical for USB 2.0 and USB using the NRZI line coding; a 0 bit is transmitted by tog- 1.x. gling the data lines from J to K or vice versa, while a 1 bit is transmitted by leaving the data lines as-is. To en- • A SuperSpeed (USB 3.0) rate of 5.0 Gbit/s. The sure a minimum density of signal transitions remains in written USB 3.0 specification was released by In- the bitstream, USB uses bit stuffing; an extra 0 bit is in- tel and its partners in August 2008. The first USB serted into the data stream after any appearance of six 3.0 controller chips were sampled by NEC in May consecutive 1 bits. Seven consecutive received 1 bits is 2009,[121] and the first products using the USB 3.0 always an error. USB 3.0 has introduced additional data specification arrived in January 2010.[122] USB 3.0 transmission encodings. connectors are generally backward compatible, but A USB packet begins with an 8-bit synchronization se- include new wiring and full duplex operation. quence '00000001'. That is, after the initial idle state J, 17

devices are also 2.0 devices. D+ Voltage signal in USB 3 uses tinned copper stranded AWG-28 cables with the differential pair D- 90±7 Ω impedance for its high-speed differential pairs Differential decoding K J K J K J K JK J K K K J J K J00 and linear feedback shift register and 8b/10b encoding NRZI decoding 0 1 0 1 1 0 1 0

Start of packet Packet ID End sent with a voltage of 1 V nominal with a 100 mV re- Packet format / clock sync (LSB first, 1010 = NAK) of packet ceiver threshold; the receiver uses .[124] SSC clock and 300 ppm precision is used. Packet headers are protected with CRC-16, while data payload is protected Example of a Negative Acknowledge packet transmitted by USB with CRC-32.[125] Power up to 3.6 W may be used. One 1.1 full-speed device when there is no more data to read. It con- unit load in superspeed mode is equal to 150 mA.[125] sists of the following fields: clock synchronization , type of packet and end of packet. Data packets would have more infor- mation between the type of packet and end of packet. 9 Transmission rates the data lines toggle KJKJKJKK. The final 1 bit (repeated K state) marks the end of the sync pattern and the begin- ning of the USB frame. For high bandwidth USB, the The theoretical maximum data rate in USB 2.0 is 480 packet begins with a 32-bit synchronization sequence. Mbit/s (60 MB/s) per controller and is shared amongst all attached devices. Some chipset manufacturers overcome A USB packet’s end, called EOP (end-of-packet), is in- this bottleneck by providing multiple USB 2.0 controllers dicated by the transmitter driving 2 bit times of SE0 (D+ within the . and D− both below max) and 1 bit time of J state. After this, the transmitter ceases to drive the D+/D− lines and According to routine testing performed by CNet, write the aforementioned pull up resistors hold it in the J (idle) operations to typical Hi-Speed (USB 2.0) hard drives can state. Sometimes skew due to hubs can add as much as sustain rates of 25–30 MB/s, while read operations are one bit time before the SE0 of the end of packet. This ex- at 30–42 MB/s;[126] this is 70% of the total available bus tra bit can also result in a “bit stuff violation” if the six bits bandwidth. For USB 3.0, typical write speed is 70–90 before it in the CRC are '1’s. This bit should be ignored MB/s, while read speed is 90–110 MB/s.[126] Mask Tests, by receiver. also known as Eye Diagram Tests, are used to determine the quality of a signal in the time domain. They are de- A USB bus is reset using a prolonged (10 to 20 millisec- fined in the referenced document as part of the electri- onds) SE0 signal. cal test description for the high-speed (HS) mode at 480 USB 2.0 devices use a special protocol during reset, Mbit/s.[127] called “chirping”, to negotiate the high bandwidth mode According to a USB-IF chairman, “at least 10 to 15 per- with the host/hub. A device that is HS capable first con- cent of the stated peak 60 MB/s (480 Mbit/s) of Hi-Speed nects as an FS device (D+ pulled high), but upon receiv- USB goes to overhead—the be- ing a USB RESET (both D+ and D− driven LOW by host tween the card and the peripheral. Overhead is a compo- for 10 to 20 ms) it pulls the D− line high, known as chirp nent of all connectivity standards”.[128] Tables illustrat- K. This indicates to the host that the device is high band- ing the transfer limits are shown in Chapter 5 of the USB width. If the host/hub is also HS capable, it chirps (re- spec. turns alternating J and K states on D− and D+ lines) let- ting the device know that the hub operates at high band- For isochronous devices like audio streams, the band- width. The device has to receive at least three sets of KJ width is constant, and reserved exclusively for a given de- chirps before it changes to high bandwidth terminations vice. The bus bandwidth therefore only has an effect on and begins high bandwidth signaling. Because USB 3.0 the number of channels that can be sent at a time, not the uses wiring separate and additional to that used by USB “speed” or latency of the transmission. 2.0 and USB 1.x, such bandwidth negotiation is not re- quired. Clock tolerance is 480.00 Mbit/s ±500 ppm, 12.000 Mbit/s ±2500 ppm, 1.50 Mbit/s ±15000 ppm. 10 Latency Though high bandwidth devices are commonly referred to as “USB 2.0” and advertised as “up to 480 Mbit/s”, For USB1 low-speed (1.5 Mbit/s) and full-speed (12 not all USB 2.0 devices are high bandwidth. The USB-IF Mbit/s) devices the shortest time for a transaction in one certifies devices and provides licenses to use special mar- direction is 1 ms.[129] USB2 high-speed (480 Mbit/s) uses keting logos for either “basic bandwidth” (low and full) or transactions within each micro frame (125 µs)[130] where high bandwidth after passing a compliance test and pay- using 1-byte interrupt packet results in a minimal re- ing a licensing fee. All devices are tested according to the sponse time of 940 ns. 4-byte interrupt packet results in latest specification, so recently compliant low bandwidth 984 ns.[131] 18 11 COMMUNICATION

11 Communication IN token expects a response from a device. The response may be a NAK or STALL response, or a DATAx frame. During USB communication data is transmitted as In the latter case, the host issues an ACK handshake if packets. Initially, all packets are sent from the host, via appropriate. An OUT token is followed immediately by the root hub and possibly more hubs, to devices. Some a DATAx frame. The device responds with ACK, NAK, of those packets direct a device to send some packets in NYET, or STALL, as appropriate. reply. SETUP operates much like an OUT token, but is used After the sync field, all packets are made of 8-bit , for initial device setup. It is followed by an eight-byte transmitted least-significant bit first. The first byte is a DATA0 frame with a standardized format. packet identifier (PID) byte. The PID is actually 4 bits; Every millisecond (12000 full-bandwidth bit times), the the byte consists of the 4-bit PID followed by its bitwise USB host transmits a special SOF (start of frame) to- complement. This redundancy helps detect errors. (Note ken, containing an 11-bit incrementing frame number in also that a PID byte contains at most four consecutive 1 place of a device address. This is used to synchronize bits, and thus never needs bit-stuffing, even when com- isochronous and interrupt data transfers. High-bandwidth bined with the final 1 bit in the sync byte. However, trail- USB 2.0 devices receive seven additional SOF tokens per ing 1 bits in the PID may require bit-stuffing within the frame, each introducing a 125 µs “microframe” (60000 first few bits of the payload.) high-bandwidth bit times each). Packets come in three basic types, each with a different USB 2.0 added PING token, which asks a device if it is format and CRC (cyclic redundancy check): ready to receive an OUT/DATA packet pair. PING is usually sent by a host when polling a device that most re- cently responded with NAK or NYET. This avoids the 11.1 Handshake packets need to send a large data packet to a device that the host suspects to be unwilling to accept it.[134] The device re- Handshake packets consist of only a single PID byte, and sponds with ACK, NAK or STALL, as appropriate. are generally sent in response to data packets. Error de- USB 2.0 also added a larger three-byte SPLIT token with tection is provided by transmitting four bits that repre- a seven-bit hub number, 12 bits of control flags, and a sent the packet type twice, in a single PID byte using five-bit CRC. This is used to perform split transactions. complemented form. Three basic types are ACK, indicat- Rather than tie up the high-bandwidth USB bus sending ing that data was successfully received, NAK, indicating data to a slower USB device, the nearest high-bandwidth that the data cannot be received and should be retried, capable hub receives a SPLIT token followed by one or and STALL, indicating that the device has an error condi- two USB packets at high bandwidth, performs the data tion and cannot transfer data until some corrective action transfer at full or low bandwidth, and provides the re- (such as device initialization) occurs.[132][133] sponse at high bandwidth when prompted by a second USB 2.0 added two additional handshake packets: NYET SPLIT token. and ERR. NYET indicates that a split transaction is not yet complete, while ERR handshake indicates that a split transaction failed. A second use for a NYET packet is to 11.3 Data packets tell the host that the device has accepted a data packet, but cannot accept any more due to full buffers. This allows A data packet consists of the PID followed by 0–1,024 a host to switch to sending small PING tokens to inquire bytes of data payload (up to 1,024 bytes for high-speed about the device’s readiness, rather than sending an entire devices, up to 64 bytes for full-speed devices, and at most unwanted DATA packet just to elicit a NAK.[132][133] eight bytes for low-speed devices),[135] and a 16-bit CRC. The only handshake packet the USB host may generate There are two basic forms of data packet, DATA0 and is ACK. If it is not ready to receive data, it should not DATA1. A data packet must always be preceded by an instruct a device to send. address token, and is usually followed by a handshake to- ken from the receiver back to the transmitter. The two packet types provide the 1-bit sequence number required 11.2 Token packets by Stop-and-wait ARQ. If a USB host does not receive a response (such as an ACK) for data it has transmitted, it Token packets consist of a PID byte followed by two pay- does not know if the data was received or not; the data load bytes: 11 bits of address and a five-bit CRC. Tokens might have been lost in transit, or it might have been re- are only sent by the host, never a device. ceived but the handshake response was lost. IN and OUT tokens contain a seven-bit device number To solve this problem, the device keeps track of the type and four-bit function number (for multifunction devices) of DATAx packet it last accepted. If it receives another and command the device to transmit DATAx packets, or DATAx packet of the same type, it is acknowledged but receive the following DATAx packets, respectively. An ignored as a duplicate. Only a DATAx packet of the op- 12.2 Ethernet 19 posite type is actually received. equipment. In the initial design, USB operated at a far If the data is corrupted while transmitted or received, the lower data rate and used less sophisticated hardware. It CRC check fails. When this happens, the receiver does was suitable for small peripherals such as keyboards and not generate an ACK, which makes the sender resend the pointing devices. packet.[136] The most significant technical differences between When a device is reset with a SETUP packet, it expects FireWire and USB include: an 8-byte DATA0 packet . • USB networks use a tiered-star topology, while USB 2.0 added DATA2 and MDATA packet types as well. IEEE 1394 networks use a tree topology. They are used only by high-bandwidth devices doing • high-bandwidth isochronous transfers that must transfer USB 1.0, 1.1 and 2.0 use a “speak-when-spoken-to” more than 1024 bits per 125 µs microframe (8,192 kB/s). protocol; peripherals cannot communicate with the host unless the host specifically requests communi- cation. USB 3.0 allows for device-initiated commu- 11.4 PRE packet nications towards the host. A FireWire device can communicate with any other node at any time, sub- Low-bandwidth devices are supported with a special PID ject to network conditions. value, PRE. This marks the beginning of a low-bandwidth • A USB network relies on a single host at the top of packet, and is used by hubs that normally do not send the tree to control the network. In a FireWire net- full-bandwidth packets to low-bandwidth devices. Since work, any capable node can control the network. all PID bytes include four 0 bits, they leave the bus in the full-bandwidth K state, which is the same as the low- • USB runs with a 5 V power line, while FireWire in bandwidth J state. It is followed by a brief pause, during current implementations supplies 12 V and theoret- which hubs enable their low-bandwidth outputs, already ically can supply up to 30 V. idling in the J state. Then a low-bandwidth packet fol- • Standard USB hub ports can provide from the typ- lows, beginning with a sync sequence and PID byte, and ical 500 mA/2.5 W of current, only 100 mA from ending with a brief period of SE0. Full-bandwidth de- non-hub ports. USB 3.0 and USB On-The-Go sup- vices other than hubs can simply ignore the PRE packet ply 1.8 A/9.0 W (for dedicated battery charging, 1.5 and its low-bandwidth contents, until the final SE0 indi- A/7.5 W Full bandwidth or 900 mA/4.5 W High cates that a new packet follows. Bandwidth), while FireWire can in theory supply up to 60 watts of power, although 10 to 20 watts is more typical. 12 Comparisons with other con- nection methods These and other differences reflect the differing de- sign goals of the two buses: USB was designed for simplicity and low cost, while FireWire was designed for high performance, particularly in time-sensitive ap- plications such as audio and video. Although similar in theoretical maximum transfer rate, FireWire 400 is faster than USB 2.0 Hi-Bandwidth in real-use,[137] es- pecially in high-bandwidth use such as external hard- drives.[138][139][140][141] The newer FireWire 800 standard is twice as fast as FireWire 400 and faster than USB 2.0 Hi-Bandwidth both theoretically and practically.[142] However, Firewire’s speed advantages rely on low-level techniques such as (DMA), which in turn have created opportunities for security exploits such as the DMA attack.

A variety of USB cables for sale in Hong Kong The chipset and drivers used to implement USB and FireWire have a crucial impact on how much of the band- width prescribed by the specification is achieved in the real world, along with compatibility with peripherals.[143] 12.1 FireWire

At first, USB was considered a complement to IEEE 1394 12.2 Ethernet (FireWire) technology, which was designed as a high- bandwidth serial bus that efficiently interconnects pe- The IEEE 802.3af Power over Ethernet (PoE) standard ripherals such as disk drives, audio interfaces, and video specifies a more elaborate power negotiation scheme than 20 14 RELATED STANDARDS

powered USB. It operates at 48 V DC and can supply power, and USB resources. more power (up to 12.95 W, PoE+ 25.5 W) over a cable eSATA, like USB, supports hot plugging, although this up to 100 meters compared to USB 2.0, which provides might be limited by OS drivers and device firmware. 2.5 W with a maximum cable length of 5 meters. This has made PoE popular for VoIP telephones, security cameras, wireless access points and other networked devices within 12.5 Thunderbolt buildings. However, USB is cheaper than PoE provided that the distance is short, and power demand is low. Thunderbolt combines PCI Express and Mini Display- Ethernet standards require electrical isolation between Port into a new serial data interface. Current Thunderbolt the networked device (computer, phone, etc.) and the implementations have two channels, each with a transfer network cable up to 1500 V AC or 2250 V DC for 60 speed of 10 Gbit/s, resulting in an aggregate unidirec- [146] seconds.[144] USB has no such requirement as it was de- tional bandwidth of 20 Gbit/s. signed for peripherals closely associated with a host com- Thunderbolt 2 uses link aggregation to combine the two puter, and in fact it connects the peripheral and host 10Gbit/s channels into one bi-directional 20Gbit/s chan- grounds. This gives Ethernet a significant safety advan- nel. tage over USB with peripherals such as cable and DSL Thunderbolt 3 is announced to use USB Type-C connected to external wiring that can assume [147][148][149] hazardous voltages under certain fault conditions.[145] connectors.

12.3 MIDI 13 Interoperability

Digital musical instruments are another example where Main article: USB adapter USB is competitive in low-cost devices. However Power over Ethernet and the MIDI plug standard have an advan- Various protocol converters are available that convert tage in high-end devices that may have long cables. USB USB data signals to and from other communications stan- can cause ground loop problems between equipment, be- dards. cause it connects ground references on both transceivers. By contrast, the MIDI plug standard and Ethernet have built-in isolation to 500V or more. 14 Related standards

12.4 eSATA/eSATAp

The eSATA connector is a more robust SATA connector, intended for connection to external hard drives and SSDs. eSATA’s transfer rate (up to 6 Gbit/s) is similar to that of USB 3.0 (up to 5 Gbit/s on current devices; 10 Gbit/s speeds via USB 3.1, announced on 31 July 2013). A de- vice connected by eSATA appears as an ordinary SATA device, giving both full performance and full compatibil- ity associated with internal drives. eSATA does not supply power to external devices. This The Wireless USB logo is an increasing disadvantage compared to USB. Even though USB 3.0’s 4.5 W is sometimes insufficient to The USB Implementers Forum is working on a wireless power external hard drives, technology is advancing and networking standard based on the USB protocol. external drives gradually need less power, diminishing the Wireless USB is intended as a cable-replacement tech- eSATA advantage. eSATAp (power over eSATA; aka nology, and uses ultra-wideband wireless technology for ESATA/USB) is a connector introduced in 2009 that sup- data rates of up to 480 Mbit/s. plies power to attached devices using a new, backward USB 2.0 High Speed Inter Chip (HSIC) is a chip-to-chip compatible, connector. On a notebook eSATAp usually variant of USB 2.0 that eliminates the conventional ana- supplies only 5 V to power a 2.5-inch HDD/SSD; on a log transceivers found in normal USB. It was adopted as a desktop workstation it can additionally supply 12 V to standard by the USB Implementers Forum in 2007. The power larger devices including 3.5-inch HDD/SSD and HSIC uses about 50% less power and 75% 5.25-inch optical drives. less board area compared to traditional USB 2.0. HSIC eSATAp support can be added to a desktop machine in uses two signals at 1.2 V and has a throughput of 480 the form of a bracket connecting to motherboard SATA, Mbit/s using 240 MHz DDR signaling. Maximum PCB 21 trace length for HSIC is 10 cm. It does not have low [8] Janssen, Cory. “What is a Universal Serial Bus (USB)?". enough latency to support RAM memory sharing between Techopedia. Retrieved 2014-02-12. two chips.[150][151] [9] Ajay Bhatt: Fellow (biography), Intel

[10] Rogoway, Mark (2009-05-09). “Intel ad campaign re- 15 See also makes researchers into rock stars”. The Oregonian. Re- trieved 2009-09-23.

• DockPort – USB 3.0, DisplayPort, audio and power [11] Pan, Hui; Polishuk, Paul (eds.). 1394 Monthly Newslet- combined in one cable ter. Information Gatekeepers. pp. 7–9. GGKEY: H5S2XNXNH99. Retrieved 2012-10-23. • Easy Transfer Cable – USB peer-to-peer transfer crossover bridge cable for Windows [12] Seebach, Peter (26 April 2005). “Standards and specs: The ins and outs of USB”. IBM. Archived from the orig- • Extensible Host Controller Interface (XHCI) inal on 2010-01-10. Retrieved 2012-09-08.

• List of computer peripheral bus bit rates [13] Universal Serial Bus Specification Revision 3.0: 3.1 (ZIP). 9 September 2011. p. 41 (3–1). Retrieved 2011-10- • LIO Unified Target (incl. , 14.08-Sep-2012 FCoE, iEEE 1394, InfiniBand, iSCSI, USB) [14] Universal Serial Bus Specification Revision 3.0: 1.6 (ZIP). • Media Transfer Protocol 9 September 2011. p. 31 (1–3). Retrieved 2011-10-14.

• Mobile High-Definition Link [15] “USB 3.0 SuperSpeed gone wild at CES 2010, trumps even your new SSD”. 9 January 2010. Retrieved 2011- 02-20.

16 Notes [16] “USB 3.0 Finally Arrives”. 11 January 2010. Retrieved 2011-02-20. [1] Up to five unit loads; in USB 1.x and 2.0, one unit load is 100 mA. [17] “SuperSpeed USB 3.0: More Details Emerge”. PC world. 6 January 2009. [2] Up to six unit loads; in USB 3.x, one unit load is 150 mA. [18] http://www.usb.org/press/USB-IF_Press_Releases/IEC_ [3] Legacy power levels with type-A to type-C cables. USB-IF_Press_Release_12.3.14_FINAL.pdf

[4] Using Type-C to Type-C cable: 1.5 A is required, while [19] http://www.usb.org/developers/ssusb/USB_3_1_ 3.0 A optional. Language_Product_and_Packaging_Guidelines_ FINAL.pdf [5] Data protocol can be either USB 3.x or 2.0. [20] http://www.usb.org/press/USB-IF_Press_Releases/ [6] With Type-AB or Type-C cable. SuperSpeedUSB_10Gbps_Available_20130731.pdf

[21] http://www.usb.org/developers/ssusb/USB_3_1_ Language_Product_and_Packaging_Guidelines_ 17 References FINAL.pdf

[1] “USB ‘A’ Plug Form Factor Revision 1.0” (PDF). USB [22] “5.5.4”. Universal Serial Bus Specification (PDF) (Tech- Implementers Forum. 23 March 2005. p. 1. Retrieved nical report). 2000. p. 40. v2.0. 2012-04-04. Body length is fully 12 mm in width by 4.5 mm in height with no deviations [23] “Difference Between USB 2.0 Full Speed and USB 2.0 High Speed Devices”. [2] “USB deserves more support”, Business, Boston Globe Online (Simson), 1995-12-31, retrieved 2011-12-12 [24] “USB Implementers Forum”.

[3] “Sony Playstation 3 60 GB”, Reviews, CNet [25] “Battery Charging v1.2 Spec and Adopters Agreement” (ZIP). USB Implementers Forum. 7 December 2010. Re- [4] “USB connector guide”. C2G. Retrieved 2013-12-02. trieved 2014-10-05.

[5] Universal Serial Bus Cables and Connectors Class Doc- [26] “USB” (PDF) (Press release). Implementers Forum. ument (PDF), Revision 2.0, USB Implementers Forum, 2008-11-17. Retrieved 2010-06-22. August 2007, p. 6, retrieved 2014-08-17 [27] “USB 3.0 Technology” (PDF). HP. 2012. Retrieved [6] “Why was mini USB deprecated in favor of Micro USB?". 2014-01-02. stackexchange.com. 2011. Retrieved 2013-12-03. [28] “Universal Serial Bus 3.0 Specification” (PDF). USB Im- [7] http://www.usb.org/developers/docs/icon_design.pdf plementers Forum. 2008-11-12. Retrieved 2012-12-29. 22 17 REFERENCES

[29] “SuperSpeed USB (USB 3.0) Performance to Double with [48] “Skype VoIP USB Installation Guide”. Retrieved 2008- New Capabilities” (PDF) (Press release). Implementers 10-30. Forum. 2013-01-06. [49] “PS/2 to USB Keyboard and Mouse Adapter”. [30] http://www.usb.org/press/USB-IF_Press_Releases/ SuperSpeedUSB_10Gbps_Available_20130731.pdf [50] “Universal Serial Bus Device Class Specification for De- vice Firmware Upgrade, Version 1.0” (PDF). USB Imple- [31] “SuperSpeed USB 10 Gbps - Ready for Development”. menters Forum. 1999-05-13. p. 7–8. Archived from the Rock Hill Herald. Retrieved 2013-07-31. original (PDF) on 2014-08-24. Retrieved 2014-09-08.

[32] “Synopsys Demonstrates Industry’s First SuperSpeed [51] “dfu-util: USB Device Firmware Upgrade tool”. fedo- USB 10 Gbps Platform-to-Platform Host-Device IP Data raproject.org. Retrieved 2014-09-08. Transfer” (Press release). Mountain View, California: Synopsys. 2013-12-10. Retrieved 2013-12-23. As mea- [52] Karsten Nohl; Sascha Krißler; Jakob Lell (2014-08-07). sured by the Ellisys USB Explorer Protocol Analyzer, the “BadUSB – On accessories that turn evil” (PDF). sr- IP realized 10 Gbps USB 3.1 effective data rates of more labs.de. Retrieved 2014-09-08. than 900 MBps between two Synopsys HAPS-70 FPGA- based prototyping systems while using backward compat- [53] Hewlett-Packard, Intel, Microsoft, NEC, ST-Ericsson, ible USB connectors, cables and software. Texas Instruments (6 June 2011). Universal Serial Bus 3.0 Specification: Revision 1.0. p. 531. Retrieved 2011-07- [33] Hruska, Joel (March 13, 2015). “USB-C vs. USB 3.1: 26. What’s the difference?". ExtremeTech. Retrieved April 9, 2015. [54] “USB 2.0 Specification Engineering Change-USB.org” (PDF). USB Flash Drive Alliance. Retrieved 2014-12- [34] Ngo, Dong. “USB Type-C: One Cable to Connect Them 29. All”. cnet.com. CNET. Retrieved 10 March 2015. [55] “Edison’s revenge”. The Economist. 2013-10-19. Re- [35] http://www.cnet.com/news/ trieved 2013-10-23. usb-type-c-one-cable-to-connect-them-all/ [56] Sam Byford (2013-12-04). “Next USB plug will finally be [36] http://www.anandtech.com/show/8377/ reversible”. The Verge. Retrieved 2013-12-04. usb-typec-connector-specifications-finalized

[37] https://intel.activeevents.com/sf14/connect/ [57] “Universal Serial Bus Cables and Connectors Class Doc- sessionDetail.ww?SESSION_ID=1254 ument Revision 2.0” (PDF). usb.org. August 2007. Re- trieved 2013-12-03. [38] http://www.anandtech.com/show/8558/ -alternate-mode-for-usb-typec-announced [58] “What is the Life Cycle of a USB Flash Drive?". Get USB. 2007-03-08. Retrieved 2011-12-12. [39] Universal Serial Bus Specification Revision 2.0 (ZIP). 11 October 2011. pp. 13; 30; 256. Retrieved 2012-09-08. [59] Quinnell, Richard A (1996). “USB: a neat package with a few loose ends”. EDN Magazine (Reed). Retrieved 2013- [40] Universal Serial Bus Specification Revision 3.0: 8.8. 9 02-18. September 2011. pp. 8–25. Archived from the original (ZIP) on 2011-11-04. Retrieved 2011-10-14.08-Sep-2012 [60] “USB 2.0 Specification Engineering Change Notice (ECN) #1: Mini-B connector” (PDF). USB-IF Develop- [41] Dan Froelich (2009-05-20). “Isochronous Protocol” ers Area. 2000-10-20. Retrieved 2014-12-11. (PDF). usb.org. Retrieved 2014-11-21. [61] “Deprecation of the Mini-A and Mini-AB Connectors” [42] “Class Codes”. USB Implementers Forum. (PDF) (Press release). USB Implementers Forum. 2007- [43] Use class information in the interface descriptors. This 05-27. Retrieved 2009-01-13. base class is defined to use in device descriptors to indi- [62] “ID Pin Resistance on Mini B-plugs and Micro B-plugs In- cate that class information should be determined from the creased to 1 Mohm”. USB IF Compliance Updates. De- Interface Descriptors in the device. cember 2009. Retrieved 2010-03-01. [44] “Universal Serial Bus Test and Measurement Class Spec- [63] “Deprecation of the Mini-A and Mini-AB Connectors” ification (USBTMC) Revision 1.0”. USB Implementers (PDF) (Press release). USB Implementers Forum. 2007- Forum. 14 April 2003. 05-23. Retrieved 2010-12-23. [45] “Universal Serial Bus Device Class Specification for De- vice Firmware Upgrade, Version 1.1” (PDF). USB Imple- [64] “Mobile phones to adopt new, smaller USB connector” menters Forum. 2004-08-05. p. 8–9. Retrieved 2014- (PDF) (Press release). USB Implementers Forum. 2007- 09-08. 01-04. Retrieved 2007-01-08.

[46] Universal Serial Bus 3.0 Specification,4.4.11 “Efficiency” [65] “Universal Serial Bus Micro-USB Cables and Connectors Specification” (PDF). USB Implementers Forum. 2007- [47] “100 Portable Apps for your USB Stick (both for Mac and 04-04. Archived from the original (PDF) on 2015-01-31. Win)". Retrieved 2008-10-30. Retrieved 2015-01-31. 23

[66] “Micro USB pinout and list of compatible smartphones [84] “7.3.2 Bus Timing/Electrical Characteristics”. Universal and other devices”. pinoutsguide.com. Serial Bus Specification. USB.org.

[67] “Universal Serial Bus Micro-USB Cables and Connec- [85] “USB.org”. USB.org. Retrieved 2010-06-22. tors Specification to the USB 2.0 Specification, Revi- sion 1.01” (PDF). USB Implementers Forum. 2007-04- [86] “Universal Serial Bus 1.1 Specification” (PDF). 07. Archived from the original (ZIP) on 2007-04-08. cs.ucr.edu. 1998-09-23. pp. 150, 158. Retrieved Retrieved 2010-11-18. Section 1.3: Additional require- 2014-11-24. ments for a more rugged connector that is durable past [87] “Universal Serial Bus 2.0 Specification, Section 7.2.1.3 10,000 cycles and still meets the USB 2.0 specification for Low-power Bus-powered Functions” (ZIP). usb.org. mechanical and electrical performance was also a consid- 2000-04-27. Retrieved 2014-01-11. eration. The Mini-USB could not be modified and remain backward compatible to the existing connector as defined [88] “Universal Serial Bus 2.0 Specification, Section 7.2.1.4 in the USB OTG specification. High-power Bus-powered Functions” (ZIP). usb.org. 2000-04-27. Retrieved 2014-01-11. [68] “OMTP Local Connectivity: Data Connectivity”. Open Mobile Terminal Platform. 17 September 2007. Re- [89] “Roundup: 2.5-inch Hard Disk Drives with 500 GB, 640 trieved 2009-02-11. GB and 750 GB Storage Capacities (page 17)". xbit- labs.com. 2010-06-16. Retrieved 2010-07-09. [69] “Universal phone charger standard approved—One-size- fits-all solution will dramatically cut waste and GHG emis- [90] “I have the drive plugged in but I cannot find the drive in sions”. ITU (press release). Pressinfo. 2009-10-22. Re- “My Computer”, why?". hitachigst.com. Retrieved 2012- trieved 2009-11-04. 03-30.

[70] “Commission welcomes new EU standards for common [91] “USB-IF Compliance Updates”. Compliance.usb.org. mobile phone charger”. Press Releases. Europa. 2010- 2011-09-01. Retrieved 2014-01-22. 12-29. Retrieved 2011-05-22. [92] “Battery Charging Specification, Revision 1.1”. USB Im- [71] New EU standards for common mobile phone charger plementers Forum. 15 April 2009. Archived from the (press release), Europa original on 29 March 2014. Retrieved 2009-09-23.

[72] The following 10 biggest mobile phone companies have [93] “The mysteries of Apple device charging”, Minty Boost, signed the MoU: Apple, LG, Motorola, NEC, Nokia, Qual- Lady Ada, 2011 comm, Research In Motion, Samsung, Sony Ericsson, Texas [94] Modify a cheap USB charger to feed an iPod, iPhone, 2013 Instruments (press release), Europa [95] Burgess, Rick. “USB 3.0 SuperSpeed update to eliminate [73] “Nice micro- Apple, now sell it everywhere”, need for chargers”. TechSpot. Giga om, 5 October 2011 [96] “USB 3.0 Promoter Group Announces Availability of [74] “Apple’s Lightning to micro-USB adapter now available USB Power Delivery Specification” (PDF). 2012-07-18. in US, not just Europe anymore”, Engadget, 2012-11-03 Retrieved 2013-01-16.

[75] “USB Pinout”. usbpinout.net. Retrieved 2014-06-23. [97] “USB Power Delivery — Introduction” (PDF). 2012-07- [76] “Proprietary Cables vs Standard USB”. anythingbuti- 16. Retrieved 2013-01-06. pod.com. 2008-04-30. Retrieved 2013-10-29. [98] “USB 3.1 Specification”. Retrieved 2014-11-11.

[77] Lex Friedman (2013-02-25). “Review: Logitech’s Ul- [99] “USB Future Specifications Industry Reviews” (PDF). trathin mini keyboard cover makes the wrong tradeoffs”. Retrieved 2014-08-10. macworld.com. Retrieved 2013-10-29. [100] “Toshiba NB200 User Manual” (PDF). UK. 2009-03-01. [78] “Universal Serial Bus Revision 3.0 Specification, Sections Retrieved 2014-01-26. 3.1.1.1 and 5.3.1.3” (ZIP). urb.org. Retrieved 2014-05- 19. [101] “USB PowerShare Feature”. dell.com. 2013-06-05. Re- trieved 2013-12-04. [79] “What is the USB 3.0 Cable Difference”. Hantat. 2009- 05-18. Retrieved 2011-12-12. [102] “USB Sleep-and-Charge Ports”. toshiba.com. Retrieved 2014-12-21. [80] “USB Cable Length Limitations” (PDF). cable- splususa.com. 2010-11-03. Retrieved 2014-02-02. [103] “USB Charge Manager”. packardbell.com. Retrieved 2014-04-25. [81] “Cables and Long-Haul Solutions”. USB FAQ. USB.org. Retrieved 2014-02-02. [104] Cai Yan (2007-05-31). “China to enforce universal cell phone charger”. EE Times. Retrieved 2007-08-25. [82] “USB Frequently Asked Questions”. USB Implementers Forum. Retrieved 2010-12-10. [105] The Chinese FCC’s technical standard: “YD/T 1591- 2006, Technical Requirements and Test Method of [83] Axelson, Jan. “USB 3.0 Developers FAQ”. Retrieved Charger and Interface for Mobile Telecommunication 2011-10-29. Terminal Equipment” (PDF) (in Chinese). Dian yuan. 24 17 REFERENCES

[106] Lam, Crystal Yan Yan; Liu, Harry Yao Hui. “How to con- [128] “USB 2.0’s Real Deal”, News & Trends, PC World, 2002- form to China’s new mobile phone interface standards”. 02-28 Wireless Net DesignLine. Retrieved 2010-06-22. [129] “Mouse stuff you ought to know about”, Urban terror, [107] “Pros seem to outdo cons in new phone charger standard”. 2008-08-09 News. 20 September 2007. Retrieved 2007-11-26. [130] Universal Serial Bus, 2011-02-01 [108] “Broad Manufacturer Agreement Gives Universal Phone Cable Green Light” (Press release). OTMP. 17 Septem- [131] Parchomov (April 2002), Real Time Control on CAN ber 2007. Retrieved 2007-11-26. (PDF), NL: U Twente

[109] “Agreement on Mobile phone Standard Charger” (Press [132] “USB Made Simple, Part 3. Data Flow”. usbmadesim- release). GSM World. ple.co.uk. 2008. Retrieved 2014-08-17.

[110] “Common Charging and Local Data Connectivity”. Open [133] “USB in a NutShell, Chapter 3. USB Protocols”. beyond- Mobile Terminal Platform. 11 February 2009. Retrieved logic.org. 2010-09-17. Retrieved 2014-08-17. 2009-02-11. [134] “Part 7, High Speed Transactions: Ping Protocol”. usb- [111] “Universal Charging Solution ~ GSM World”. GSM madesimple.co.uk. 2008. Retrieved 2014-08-16. world. Retrieved 2010-06-22. [135] “USB in a NutShell”. Chapter 4 - Endpoint Types. Re- trieved 2014-09-05. [112] “Meeting the challenge of the universal charge standard in mobile phones”. Planet Analog. Retrieved 2010-06-22. [136] “Debugging Common USB Issues”. Retrieved 2013-06- 05. [113] “The Wireless Association Announces One Universal Charger Solution to Celebrate Earth Day” (Press release). [137] “FireWire vs. USB 2.0” (PDF). QImaging. Retrieved CTIA. 2009-04-22. Retrieved 2010-06-22. 2010-07-20.

[114] “ITU” (Press release). 2009-10-22. Retrieved 2010-06- [138] “FireWire vs. USB 2.0 – Bandwidth Tests”. Retrieved 22. 2007-08-25.

[115] “chargers”. EU: EC. 2009-06-29. Retrieved 2010-06-22. [139] “USB 2.0 vs FireWire”. Digit-Life. Retrieved 2007-08- 25. [116] “Europe gets universal cellphone charger in 2010”. Wired. 2009-06-13. Retrieved 2010-06-22. [140] Metz, Cade (2003-02-25). “The Great Interface-Off: FireWire Vs. USB 2.0”. PC Magazine. Retrieved 2007- [117] “One size-fits-all mobile phone charger: IEC publishes 08-25. first globally relevant standard”. International Elec- trotechnical Commission. 2011-02-01. Retrieved 2012- [141] Heron, Robert. “USB 2.0 Versus FireWire”. TechTV. 02-20. Retrieved 2007-08-25.

[118] “Part 2 - Electrical”. MQP Electronics Ltd. Retrieved [142] “FireWire vs. USB 2.0”. USB Ware. Retrieved 2007-03- 2014-12-29. 19.

[119] “Watt to Know About iPhone & iPad Power Adapters | [143] Key, Gary (2005-11-15). “Firewire and USB Perfor- Analysis”. The Mac Observer. Retrieved 2011-12-12. mance”. Retrieved 2008-02-01.

[120] “Nook Color charger uses special micro-USB connector”. [144] “802.3, Section 14.3.1.1” (PDF). IEEE. barnesandnoble.com. 2011-07-03. [145] “Powerbook Explodes After Comcast Plugs In Wrong Ca- [121] “NEC ready to sample 'world’s first' USB 3.0 controller ble”. Consumerist. 2010-03-08. Retrieved 2010-06-22. chip”. Retrieved 2009-06-15. [146] “How Thunderbolt Technology Works: Thunderbolt [122] “When will USB 3.0 products hit the market?". Retrieved Technology Community”. Thunderbolttechnology.net. 2009-05-11. Retrieved 2014-01-22.

[123] “USB in a NutShell—Chapter 2—Hardware”. Beyond [147] One port to rule them all: Thunderbolt 3 and USB Type-C Logic.org. Retrieved 2007-08-25. join forces, retrieved 2015-06-02

[124] “Technical Specifications of the USB 3.0 SuperSpeed Ca- [148] Thunderbolt 3 is twice as fast and uses reversible USB-C, bles”. 100717 usb3.com retrieved 2015-06-02

[125] “Universal Serial Bus 3.0 Specification, Rev 1.0 Novem- [149] Thunderbolt 3 embraces USB Type-C connector, doubles ber 12, 2008” (PDF). 100717 usb3.com bandwidth to 40Gbps, retrieved 2015-06-02

[126] “Seagate FreeAgent GoFlex Ultra-portable” (review). [150] “Interchip Connectivity: HSIC, UniPro, HSI, C2C, LLI... CNet. Retrieved 2011-05-22. oh my!". Retrieved 2011-06-24.

[127] Schwarz, Rohde (2012-05-25). “USB 2.0 Mask Testing” [151] “USB High Speed Inter-Chip Interface”. Retrieved 2011- (PDF). Retrieved 2012-07-12. 06-24. 25

18 Further reading

• Axelson, Jan (1 September 2006). USB Mass Stor- age: Designing and Programming Devices and Em- bedded Hosts (1st ed.). Lakeview Research. ISBN 978-1-931-44804-8. 287 pp. • ——— (1 December 2007). Complete: COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems (2nd ed.). Lakeview Research. ISBN 978-1-931-44806-2. 380 pp.

• ——— (2015). USB Complete: The Developer’s Guide (5th ed.). Lakeview Research. ISBN 978- 1-931448-28-4. 524 pp. • Hyde, John (February 2001). USB Design by Exam- ple: A Practical Guide to Building I/O Devices (2nd ed.). Intel Press. ISBN 978-0-970-28465-5. 510 pp. • “Debugging USB 2.0 for Compliance: It’s Not Just a Digital World” (PDF). Technologies Application Note (1382–3). Agilent..

19 External links

• “USB Implementers Forum”. • “Universal Host Controller Interface (UHCI)" (PDF). Intel.

• “USB 3.0 Standard-A, Standard-B, Powered-B con- nectors”. Pinouts guide.

• “Characterization and compliance test”. Agilent. • Muller, Henk. “How To Create And Program USB Devices,” Electronic Design, July 2012 • An Analysis of Throughput Characteristics of Uni- versal Serial Bus, June 1996, by John Garney • USB 2.0 Protocol Engine, October 2010, by Razi Hershenhoren and Omer Reznik • Universal serial bus interfaces for data and power:

• IEC 62680-1:2013 Part 1: Universal serial bus specification, revision 2.0 • IEC 62680-2:2013 Part 2: Universal serial bus - Micro-USB cables and connectors specifica- tion, revision 1.01 • IEC 62680-3:2013 Part 3: USB Battery Charging Specification, revision 1.2 26 20 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

20 Text and image sources, contributors, and licenses

20.1 Text

• USB Source: http://en.wikipedia.org/wiki/USB?oldid=666164416 Contributors: Damian Yerrick, AxelBoldt, Derek Ross, Bryan Derk- sen, Tarquin, Stephen Gilbert, Taw, Ed Poor, Aldie, SimonP, Maury Markowitz, Azhyd, Rcingham, Heron, Leandrod, Agitate, Bde- sham, Michael Hardy, Modster, DopefishJustin, Fuzzie, Gregben~enwiki, Norm, Nixdorf, Gabbe, Ixfd64, Eurleif, Dori, Mcarling, Paul A, Ee79, CesarB, Egil, Ahoerstemeier, Stan Shebs, Mac, Lovely Chris, Nanshu, Humanoid, Angela, Den fjättrade ankan~enwiki, Tsk~enwiki, Julesd, Glenn, Scott, Harvester, Ed Brey, Ehn, CAkira, Mulad, Feedmecereal, Guaka, Crissov, Timwi, Tacvek, Ww, Dysprosia, Wolf- gang Kufner, Andrewman327, Gutza, Doradus, PeterGrecian, Radiojon, Espertus, Pedant17, Tpbradbury, Maximus Rex, Grendelkhan, Saltine, Taxman, Fibonacci, Omegatron, Ed g2s, Thue, Wonko, Fvw, Capbat, Jeffq, Chuunen Baka, EpiVictor, Robbot, Paranoid, Blugill, Mazin07, Hankwang, Chealer, Fredrik, Kristof vt, Vespristiano, RedWolf, Peak, Dittaeva, Nurg, Romanm, Richardpitt, Lowellian, Rfc1394, Academic Challenger, Spike, SchmuckyTheCat, Gidonb, Zidane2k1, Mushroom, Lupo, Arm, Asparagus, Enochlau, Dave6, Pabouk, Giftlite, Smjg, DocWatson42, Brouhaha, MaGioZal, Christopher Parham, Wizzy, DavidCary, Fudoreaper, BenFrantzDale, Kenny sh, Cobaltbluetony, Joaopaulo1511, Karn, Peruvianllama, Ds13, Everyking, Filceolaire, Alexander.stohr, Pietz, Whitis, Rchandra, Be- sigedB, AlistairMcMillan, Khalid hassani, Matt Crypto, Spe88, PlatinumX, Pne, Bobblewik, Tagishsimon, Golbez, Mobius, Nlaporte, Wmahan, Munge, Chowbok, Simulcra, Utcursch, Pgan002, Jonathan Grynspan, Jonel, Sonjaaa, Quadell, Antandrus, HorsePunchKid, Beland, Neilm, Ctachme, OverlordQ, Dnas, Kiteinthewind, Jossi, Pembers, Wehe, Grauw, Oneiros, Ilgiz, Baricom, Jesster79, KVeil, My- sidia, Icairns, Sam Hocevar, Gschizas, Sillydragon, Tooki, Urhixidur, Mschlindwein, Quota, M1ss1ontomars2k4, Moxfyre, EagleOne, DmitryKo, Rpkrawczyk, SimonEast, Rfl, Wikkrockiana, Archer3, Imroy, CALR, JTN, Qk~enwiki, Noisy, Discospinster, Rich Farm- brough, Rhobite, FT2, Pmsyyz, Hcs, Deh, Pie4all88, ArnoldReinhold, Smyth, Kooo, Filzstift, Xezbeth, Mjpieters, NickVeys, Alistair1978, Dolda2000, Maaf, IanGM, Kbh3rd, S.K., Plugwash, Evice, Allesbehalve~enwiki, RJHall, Uwe Hermann, Lankiveil, Hayabusa future, Jarfil, Yitzhak, Shamilton, Sietse Snel, Nrbelex, Theshowmecanuck, Aaronbrick, Jpgordon, Adambro, Gyll, Bobo192, Nigelj, Kghose, O18, Fir0002, DigitalAvatar, Func, SnowRaptor, Polluks, Brim, MaxHund, Johnteslade, Cwolfsheep, Giraffedata, Homerjay, Scollk, Kjkolb, Nk, Waltervulej, Sleske, Hargrimm, John Fader, Novakreo, Jonathunder, Hooperbloob, Nsaa, Olekrst, Jason One, Lawpjc, Shir- imasen, Storm Rider, Danski14, Honeycake, Alansohn, T4bits, Transfinite, Elpincha, Walter Görlitz, Falsifian, Thechuck, Gssq, Atlant, Jeltz, Jezmck, Andrewpmk, Hopp, Bz2, Ahruman, Zippanova, Apoc2400, Nasukaren, Psz, Sligocki, Cadre, Kocio, Antialias, Theodore Kloba, Hohum, Lugevas, Wtmitchell, Ronark, Isaac, SidP, Rebroad, ProhibitOnions, Wtshymanski, Stephan Leeds, Jwinius, H2g2bob, JonSangster, BDD, TrickyNik, SteinbDJ, Ringbang, Algocu, Netkinetic, Kazvorpal, Dan100, CINCABF, Btornado, Ling Kah Jai, Za- kuSage, Kbolino, Vanished user dfvkjmet9jweflkmdkcn234, Kenyon, Zntrip, DenisYurkin, KUsam, Brycen, Bobrayner, Woohookitty, Poppafuze, Linas, Katyare, Sfoehner, Rocastelo, Thorpe, James Kemp, Gordeonbleu, Armando, Pol098, Windsok, JeremyA, Riumplus, Hdante, Pchov, Davidfstr, GregorB, Eyreland, Odam, Hughcharlesparker, Bruns, DocRuby, Bubeck, Outlyer, DavidFarmbrough, Brown- steve, Icydid, Mirddes, Jimgawn, Emerson7, Danbee, MrSomeone, Hideyuki, MassGalactusUniversum, E090, Buxtehude, A Train, Elvey, Raymond Hill, Yurik, Reisio, Mendaliv, Snafflekid, Pmj, Josh Parris, Tbird20d, Coneslayer, Rjwilmsi, Seidenstud, Jake Wartenberg, Joel D. 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MER-C, Sonicsuns, Mcorazao, Lesiz, Ghartwig, Shayno, H3llbringer, Mwarren us, Uisqebaugh, PhilKnight, Savant13, Steveprutz, .ana- condabot, Geniac, Yosh3000, GoldKanga, OllyH, Pedro, Bongwarrior, VoABot II, TiffaF, Eus Kevin, Maxwellversion2, Andreweaton, Wik- ifan21century, Nw15062, AMK1211, Pugetbill, CTF83!, Wabernat, Adot, Becksguy, KJRehberg, SwiftBot, Rohasnagpal, D zone, Sven Godin, Mkdw, Allstarecho, LorenzoB, MCG, Enquire, Chris G, JaGa, Kniesten, Inclusivedisjunction, Phip, Calltech, Quizzicus, 0612, Grand Am, Don-vip, Stephenchou0722, JosephCampisi, Ryper, MartinBot, JCLAWSON, Axlq, Jim.henderson, Naohiro19, Nikpapag, CableCat, Givemeornot, MNAdam, Robijn, Zlhappyone, Padillah, R'n'B, CommonsDelinker, Truerock2, Siliconov, JLuna103, Tgeairn, Ceros, J.delanoy, Mange01, ChrisFAF, Mrtangent, Hans Dunkelberg, Jim A H, Darkride, Kemiv, Jesant13, Ginsengbomb, Mike.lifeguard, Atamido, R!SC, Mamyles, Matta33178, Gblandst, Nubi78, UdovdM, Dispenser, Asbjornu, DarkFalls, Pinkcious, McSly, K8 fan, Jim-Bob Harris, Servel333, Osndok, Arlie davis, Stacrd, Aforallie, RoninRVP, Manassehkatz, Hduckman, KylieTastic, My man Friday, Comet- styles, JtMinahan, Spartan117458, Tweisbach, Remember the dot, Benignbala, Marstronix, AggroBoy, Yanayz, Torturetyler, Ajfweb, Jay- the-mad'n, Hellgi, Black Walnut, Andy Marchbanks, Rob Cranfill, Useight, Tkgd2007, Suvituuli, Mlewis000, Idioma-bot, Baoap~enwiki, Thals1992, Joeinwap, Jmcdon10, Boijunk, X!, NZR~enwiki, UnicornTapestry, VolkovBot, Praveentech, Meaningful Username, The Wild Falcon, DSRH, Anibius, RingtailedFox, Zenotek, Jmrowland, Imperator3733, AlnoktaBOT, Darkdawn75, VasilievVV, MenasimBot, So- liloquial, TobyDZ, 132qwerty, Classical geographer, Epson291, Doc Magnus, Sdsds, Philip Trueman, Mun206, TXiKiBoT, Thomas d stewart, Dwight666, Technopat, NipokNek, GDonato, Midlandstoday, Julienrl, Koopa turtle, JayC, Devin6687, Qxz, Someguy1221, Scuac, Nchalada, Owengibbins, Gaius619, Corvus cornix, Cootiequits, DenisBlanchette, 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abi, Svick, JohnSawyer, Dcook32p, Aleksandrit, Wiknerd, Bestalex, Fishnet37222, Pinkadelica, GioCM, Wjwalrus, C0nanPayne, Asigler, Floorwalker, Atif.t2, RegentsPark, Martarius, De728631, Iloveandersoncooper, ClueBot, Samuel Grant, Tim Forcer, Zeptomoon, Drdomestod, Foxj, Wikievil666, The Thing That Should Not Be, Eric Wester, Lockoom, Shniken1, Compellingelegance, Kendo70133, Ant75, B. van der Wee, Timaru, Quinxorin, Nikkibella21, Gaia Octavia Agrippa, Iandiver, Imotor, Reeceyyyy15, 4176shelton, Mild Bill Hiccup, Boing! said Zebedee, Iuhkjhk87y678, Niceguyedc, Nullaman, Markstuart44, Mid- MadWiki, Hansschulze, LizardJr8, Yuckhil, Shjacks45, Akasnakeyes, Kittens-Pedro, Ridge Runner, Dirtyfrank10, Rprpr, Whompage, Puchiko, 718 Bot, Pointillist, DerekMorr, Manishearth, Tomlee1968, Skylinerspeeder, DragonBot, Asafoot, Kitsunegami, Ktr101, Ex- cirial, Diderot’s dreams, Alexbot, Crywalt, Waiwai933, Goodone121, Toddinpal, Timhoppen, Flightsoffancy, Bender2k14, Rwestafer, Muhandes, BdON003, A 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aoiowaiuyr894isdik43, Chronulator, Odatus, Ross5647, Lada103, Reach Out to the Truth, Mirabilos, ArwinJ, RjwilmsiBot, Parmastew, Ahivarn, Ripchip Bot, Gregsea, Airsplit, Beleg Tâl, Lopifalko, Usb3o, Salvio giuliano, Rollins83, DASHBot, Drewdc90, Wiki777777ikiw, EmausBot, John of Reading, WikitanvirBot, Avenue X at Cicero, Qasimnb, Immunize, Z hosen, Dltwaddell, Bdijkstra, Aaweisen, Dewritech, GoingBatty, RA0808, Ebe123, CannonR, Xmm0, Tommy2010, Jaywalk3r, Mayhemm, Atalsandip, Brenbren92, Graglin, Bssasidhar, AaronLLF, Asetwofifty, Jargoness, Marcfl, Traxs7, Modestginger, Veejayyc, MithrandirAgain, A0183305, Atenor1932, Pushpinder86, MSR93, Access Denied, H3llBot, Colinkgl, Caspertheghost, Idabag, Sorter, Seanmcd27, R2D2 C3PO R2D2, Sbmeirow, Viljo Viitanen, Coasterlover1994, Dmlmax, L Kens- ington, Mad with power, Palosirkka, MWisBest, Bstard12, Daft Creftsman, Mcmaven2, Carmichael, Burrin.p, Toyotatundra, GermanJoe, SuperBeav, Evan-Amos, Wtf305, Xyzzyavatar, Bobbb53, Timm123, Manuactive, 28bot, Cgumas, Hlandro77, Georgy90, Diamondland, SpadesSlick, Mikhail Ryazanov, ClueBot NG, Cwmhiraeth, Galilsnap, Vippylaman, Matthiaspaul, MelbourneStar, Vuongfat, Rufflos, Dwdrinnan, Amr.rs, Frietjes, Cntras, Shafkatsharif, O.Koslowski, The guy who kleanz, Widr, Reify-tech, Agilent.Showard, Concen- trate2, Jmayorga5, The.Computer1, Helpful Pixie Bot, Voeren, RadioactiveKiller1, Compilation finished successfully, පසිඳු කාවින්ද, Curb Chain, Strike Eagle, Wbm1058, Sweeet ann, WNYY98, Littlefdsa, Lowercase sigmabot, Gauravsangwan, BG19bot, Gryffon5147, Ami- Ayalon1969, Baqeri1, Arnavchaudhary, Coolstr24, KShiger, Asim mahakul, Remove indian propaganda, Heaveen, Tiscando, Akkazemi, GKFX, Niceter, Chirry2011, IAMBATMANDEALWITHIT, Compfreak7, Hobofixer, Eye of God, Austinv311, Yowanvista, LorLeod, Wikiwinganer, Azuosdativa, Ste.virus, RadicalRedRaccoon, Zedtwitz, Zedshort, Bill Evans at Mariposa, Glacialfox, Jkl4201, 220 of Borg, Vlooo, BillBucket, Sajajaja, Anbu121, Strz4life, IRedRat, BattyBot, Jewremy, DigitalMediaSage, Lilash12132, Tom812, Nithin.A.P, Jimw338, Dry Erase Markers, TehMulti, Psmith781, Jerriskirkwood, Jionpedia, Khazar2, Iredfj, 786b6364, EagerToddler39, Dexbot, EliasOenal, Mogism, Jackintosh11, Wiki nol ege, Frosty, Makcal94, Bashirmja, Wywin, Trackunf, Vahid alpha, BurritoBazooka, Joe- 28 20 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

fish13, USB lover 101, Espelp, Jonney2000, Evamy~enwiki, Acetotyce, Howicus, Akhan peri, Leandrogfcdutra, Lorondos, Arabfaculty, Comp.arch, VirtualAssist, Funlunde3, Ginsuloft, Someone not using his real name, NATLANDAU, Focusonpc, Werddemer, Aluxosm, Karanjag, Zedgearia, Atheeb Israr, Korey.conway, Bokwai914, Njol, MooImAFox, Ali.Zeineddine93, Sofia Lucifairy, ShaunRoselt, Hk- coms, Catlover66667, Problemlow, Monkbot, King of Arabia, Qwertyxp2000, Billywanta, RoundupResistance, Nullptr, Cory.stewart, ChamithN, Netsurfer912, Motley123, Bpmeller, Jminer7, GiantRooster64, RaggaBomb1, Kiirunaps, ToonLucas22, Spankaliciousmyh1, Stego27, Jacob Staff, Tony62791028, Ruftas, So-retro-it-hurts, Agencjareklamowa, Eldizzino and Anonymous: 2243

20.2 Images

• File:A_Micro-A_USB_port.jpeg Source: http://upload.wikimedia.org/wikipedia/commons/3/31/A_Micro-A_USB_port.jpeg License: CC BY-SA 3.0 Contributors: Own work Original artist: User:heaveen • File:Cables_in_Hong_Kong.JPG Source: http://upload.wikimedia.org/wikipedia/commons/8/86/Cables_in_Hong_Kong.JPG License: CC BY-SA 3.0 Contributors: Own work Original artist: Victorgrigas • File:Certified_Hi-Speed_USB.svg Source: http://upload.wikimedia.org/wikipedia/commons/c/c8/Certified_Hi-Speed_USB.svg Li- cense: Public domain Contributors: http://brandsoftheworld.com/search/?query_id=3996676&page=1&mtype=&brand_id=22618 Orig- inal artist: Certified Hi-Speed USB • File:Certified_Wireless_USB.svg Source: http://upload.wikimedia.org/wikipedia/en/3/32/Certified_Wireless_USB.svg License: ? Con- tributors: http://brandsoftheworld.com/search/?query_id=3996676&page=1&mtype=&brand_id=143161 Original artist: ? • File:Circuit_board_from_a_USB_3.0_external_2.5-inch_HDD_enclosure.jpg Source: http://upload.wikimedia.org/wikipedia/ commons/9/94/Circuit_board_from_a_USB_3.0_external_2.5-inch_HDD_enclosure.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Dsimic • File:Commons-logo.svg Source: http://upload.wikimedia.org/wikipedia/en/4/4a/Commons-logo.svg License: ? Contributors: ? Original artist: ? • File:Computer-USB2-card.jpg Source: http://upload.wikimedia.org/wikipedia/commons/8/89/Computer-USB2-card.jpg License: Public domain Contributors: Own work Original artist: Evan-Amos • File:Computer-aj_aj_ashton_01.svg Source: http://upload.wikimedia.org/wikipedia/commons/c/c1/Computer-aj_aj_ashton_01.svg License: CC0 Contributors: ? Original artist: ? • File:Connector_USB_3_IMGP6017_wp.jpg Source: http://upload.wikimedia.org/wikipedia/commons/1/17/Connector_USB_3_ IMGP6017_wp.jpg License: FAL Contributors: Own work Original artist: smial (talk) • File:Connector_USB_3_IMGP6024_wp.jpg Source: http://upload.wikimedia.org/wikipedia/commons/7/75/Connector_USB_3_ IMGP6024_wp.jpg License: FAL Contributors: Own work Original artist: smial (talk) • File:Connector_USB_3_IMGP6033_wp.jpg Source: http://upload.wikimedia.org/wikipedia/commons/c/c3/Connector_USB_3_ IMGP6033_wp.jpg License: FAL Contributors: Own work Original artist: smial (talk) • File:Folder_Hexagonal_Icon.svg Source: http://upload.wikimedia.org/wikipedia/en/4/48/Folder_Hexagonal_Icon.svg License: Cc-by- sa-3.0 Contributors: ? Original artist: ? • File:Male_and_Female_USB_Connectors.jpg Source: http://upload.wikimedia.org/wikipedia/commons/a/a5/Male_and_Female_ USB_Connectors.jpg License: CC-BY-SA-3.0 Contributors: Transferred from en.wikipedia; transfer was stated to be made by User:eptalon. Original artist: Original uploader was Zephyris at en.wikipedia Later version(s) were uploaded by Osama bin dipesh at en.wikipedia. • File:MicroB_USB_Plug.jpg Source: http://upload.wikimedia.org/wikipedia/commons/d/db/MicroB_USB_Plug.jpg License: CC BY- SA 3.0 Contributors: Own work Original artist: User:masamic • File:Micro_USB_phone_charger.jpg Source: http://upload.wikimedia.org/wikipedia/commons/7/7c/Micro_USB_phone_charger.jpg License: Public domain Contributors: Own work Original artist: Reinraum • File:Mini_usb_AB.jpg Source: http://upload.wikimedia.org/wikipedia/commons/a/ad/Mini_usb_AB.jpg License: CC BY 2.5 Contribu- tors: ? Original artist: User Mgdunn on en.wikipedia • File:Nuvola_apps_ksim.png Source: http://upload.wikimedia.org/wikipedia/commons/8/8d/Nuvola_apps_ksim.png License: LGPL Contributors: http://icon-king.com Original artist: David Vignoni / ICON KING • File:Question_book-new.svg Source: http://upload.wikimedia.org/wikipedia/en/9/99/Question_book-new.svg License: Cc-by-sa-3.0 Contributors: Created from scratch in Adobe Illustrator. Based on Image:Question book.png created by User:Equazcion Original artist: Tkgd2007 • File:SanDisk_Cruzer_Micro.png Source: http://upload.wikimedia.org/wikipedia/commons/8/86/SanDisk_Cruzer_Micro.png License: Public domain Contributors: This file was derived from: Usb-thumb-drive.jpg Original artist: Original: Evan-Amos

• File:SuperSpeed_USB.svg Source: http://upload.wikimedia.org/wikipedia/commons/0/0c/SuperSpeed_USB.svg License: Public domain Contributors: http://www.usb.org Original artist: Originally uploaded by Caspertheghost at en.wikipedia • File:Thinkpad_X220_Yellow_USB.jpg Source: http://upload.wikimedia.org/wikipedia/commons/d/d8/Thinkpad_X220_Yellow_USB. jpg License: CC BY-SA 3.0 Contributors: I took this photo as an example of a sleep and charge USB port. Original artist: Sasawat at English Wikipedia 20.2 Images 29

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