Universal Serial Bus

Infobox Computer Hardware Bus
name = USB
fullname = Universal Serial Bus

---

caption = Original USB Logo
invent-date = January 1996
width = 1
numdev = 127 per host controller
speed = 12 or 480 Mbit/s (1.5 to 60 MByte/s)
style = s
hotplug = Yes
external = Yes

In information technology, Universal Serial Bus (USB) is a serial bus standard to interface devices to a host computer. USB was designed to allow many peripherals to be connected using a single standardized interface socket and to improve the plug-and-play capabilities by allowing hot swapping, that is, by allowing devices to be connected and disconnected without rebooting the computer or turning off the device. Other convenient features include providing power to low-consumption devices without the need for an external power supply and allowing many devices to be used without requiring manufacturer specific, individual device drivers to be installed.

USB is intended to replace many legacy varieties of serial and parallel ports. USB can connect computer peripherals such as mouse, keyboards, PDAs, gamepads and joysticks, scanners, digital cameras, printers, personal media players, and flash drives. For many of those devices USB has become the standard connection method. USB was originally designed for personal computers, but it has become commonplace on other devices such as PDAs and video game consoles, and as a bridging power cord between a device and an AC adapter plugged into a wall plug for charging purposes. As of 2008, there are about 2 billion USB devices in the world. [cite web |url=http://www.usb.org/developers/wusb/ |title=Wireless USB from the USB-IF |accessdate=2008-05-30]

The design of USB is standardized by the USB Implementers Forum (USB-IF), an industry standards body incorporating leading companies from the computer and electronics industries. Notable members have included Agere (now merged with LSI Corporation), Apple Inc., Hewlett-Packard, Intel, NEC, and Microsoft.

History

The USB 1.0 specification model was introduced in November 1995. USB was created by the Core group of companies that consisted of Intel, Compaq, Microsoft, Digital, IBM, and Northern Telecom. Intel produced the UHCI host controller and open software stack; Microsoft produced a USB software stack for Windows and co-authored the OHCI host controller specification with National Semicondutor and Compaq; Philips produced early USB-Audio; and TI produced the most widely used hub chips. Originally USB was intended to replace the multitude of connectors at the back of PCs, as well as to simplify software configuration of communication devices.

The original Apple "Bondi blue" iMac G3, introduced May 6, 1998, was the first computer to offer USB ports without offering "legacy" ports [ [http://www.ibm.com/developerworks/power/library/pa-spec7.html IBM - The ins and outs of USB] ] [ [http://support.apple.com/specs/imac/iMac.html iMac - Technical Specification] ] . USB 1.1 came out in September 1998 to help rectify the adoption problems that occurred with earlier iterations of USB, mostly those relating to hubs. [ [http://www.ibm.com/developerworks/power/library/pa-spec7.html Standards and specs: The ins and outs of USB] ]

As of 2008, the USB specification is at version 2.0 (with revisions). Hewlett-Packard, Intel, Lucent (now LSI Corporation since its merger with Lucent spinoff Agere Systems), Microsoft, NEC, and Philips jointly led the initiative to develop a higher data transfer rate than the 1.1 specification. The USB 2.0 specification was released in April 2000 and was standardized by the USB-IF at the end of 2001. Equipment conforming with any version of the standard will also work with devices designed to any previous specification (known as backward compatibility).

Overview

A USB system has an asymmetric design, consisting of a host, a multitude of downstream USB ports, and multiple peripheral devices connected in a tiered-star topology. Additional USB hubs may be included in the tiers, allowing branching into a tree structure with up to five tier levels . A USB host may have multiple host controllers and each host controller may provide one or more USB ports. Up to 127 devices, including the hub devices, may be connected to a single host controller.

USB devices are linked in series through "hubs". There always exists one hub known as the root hub, which is built-in to the host controller. So-called "sharing hubs", which allow multiple computers to access the same peripheral device(s), also exist and work by switching access between PCs, either automatically or manually. They are popular in small-office environments. In network terms, they converge rather than diverge branches.

A physical USB device may consist of several logical sub-devices that are referred to as "device functions". A single device may provide several functions, for example, a webcam (video device function) with a built-in microphone (audio device function).

USB device communication is based on "pipes" (logical channels). Pipes are connections from the host controller to a logical entity on the device named an "endpoint". The term "endpoint" is also occasionally used to refer to the pipe. A USB device can have up to 32 active pipes, 16 into the host controller and 16 out of the controller. Each endpoint can transfer data in one direction only, either into or out of the device, so each pipe is uni-directional. Endpoints are grouped into "interfaces" and each interface is associated with a single device function. An exception to this is endpoint zero, which is used for device configuration and which is not associated with any interface.

When a new USB device is connected to a USB host, the "USB device enumeration" process is started. The enumeration process first sends a reset signal to the USB device. The speed of the USB device is determined during the reset signaling. After reset, USB device setup information is read from the device by the host and the device is assigned a unique host-controller-specific 7-bit address. If the device is supported by the host, the device drivers needed for communicating with the device are loaded and the device is set to configured state. If the USB host is restarted, the enumeration process is repeated for all connected devices.

The host controller polls the bus for traffic, usually in a Round-robin fashion, so no USB device can transfer any data on the bus without an explicit request from the host controller.

Host controllers

The computer hardware that contains the host controller and the root hub has an interface geared toward the programmer which is called "Host Controller Device" (HCD) and is defined by the hardware implementer.

In the version 1.x age, there were two competing HCD implementations, "Open Host Controller Interface" (OHCI) and "Universal Host Controller Interface" (UHCI). OHCI was developed by Compaq, Microsoft and National Semiconductor; UHCI was by Intel.
VIA Technologies licensed the UHCI standard from Intel; all other chipset implementers use OHCI. UHCI is more software-driven, making UHCI slightly more processor-intensive than OHCI but cheaper to implement. The dueling implementations forced operating system vendors and hardware vendors to develop and test on both implementations, which increased cost.

HCD standards are out of the USB specification's scope, and the USB specification does not specify any HCD interfaces. In other words, USB defines the format of data transfer through the port, but not the system by which the USB hardware communicates with the computer it sits in.

During the design phase of USB 2.0, the USB-IF insisted on only one implementation. The USB 2.0 HCD implementation is called the "Enhanced Host Controller Interface" (EHCI). Only EHCI can support hi-speed (480 Mbit/s) transfers. Most of PCI-based EHCI controllers contain other HCD implementations called 'companion host controller' to support Full Speed (12 Mbit/s) and may be used for any device that claims to be a member of a certain class. An operating system is supposed to implement all device classes so as to provide generic drivers for any USB device. Device classes are decided upon by the Device Working Group of the USB Implementers Forum.

Device classes include: [ [http://www.usb.org/developers/defined_class USB Class Codes] at USB.org]

In addition to these cable assemblies also a cable with Micro-A and Standard-A receptacle is compliant with USB specifications. Other combinations of connectors are not compliant. However, some older devices and cables with Mini-A connector have been certified by USB-IF; the Mini-A connector has been deprecated, and no new certification for assemblies using Mini-A connector will be allowed. [ [http://www.usb.org/developers/Deprecation_Announcement_052507.pdf Deprecation announcement of Mini-A and Mini-AB connectors by USB Implementers Forum Administration] ]

Note: NS is non-standard, existing for specific proprietary purposes not at the guidance of the USB-IF.

Types of USB connector

There are several types of USB connectors, including some that have been added as the specification has progressed. The original USB specification detailed Standard-A and Standard-B plugs and receptacles. The first engineering change notice to the USB 2.0 specification added Mini-B plugs and receptacles. The data slots in the A - Plug are actually farther in the plug than the outside power wires to prevent data errors by powering the device first, then transferring data.

The Standard-A type of USB connectors takes on the appearance of flattened rectangles that plugs into downstream-port sockets on the USB host or a hub. This kind of connector is most frequently seen on cables that are permanently attached to a device, such as one on a cable that connects a keyboard or mouse to the computer. Standard-B connectors looks square with beveled corners, and plugs into upstream sockets on devices and hubs. The Standard-B connector is mainly used only for the device end of a removable cable, such as between a hub and a printer. This two-connector scheme prevents a user from accidentally creating a loop. [cite web
last = Quinnell
first = Richard A
authorlink =
coauthors =
title =USB: a neat package with a few loose ends - USB Fundamentals
work =
publisher = EDN Magazine of Reed Properties Inc
date = 1996
url = http://www.edn.com/archives/1996/102496/df_01.htm#USB%20fundamentals
accessdate = 2008-08-06]

The non-standard Mini-USB's, official Mini-B, Micro-A, and Micro-B connectors are used for smaller devices such as PDAs, mobile phones or digital cameras. The Standard-A plug is approximately 4 by 12 mm, the Standard-B approximately 7 by 8 mm, and the Mini-A and Mini-B plugs approximately 2 by 7 mm.

The Micro-USB connector, was announced by the USB-IF on January 4, 2007. [cite press release| publisher = USB Implementers Forum | title = Mobile phones to adopt new, smaller USB connector | date = 2007-01-04| accessdate= 2007-01-08| url= http://www.usb.org/press/pressroom/2007_01_04_usbif.pdf |format=PDF] It is intended to replace the Mini-USB plugs used in many new smartphones and Personal digital assistants. This Micro-USB plug is rated for 10,000 connect-disconnect cycles. It is about half the height of the mini-USB connector, but features a similar width. In the "Universal Serial Bus Micro-USB Cables and Connectors Specification", details have been laid down for Micro-A plugs, Micro-AB receptacles, and Micro-B plugs and receptacles, along with a Standard-A receptacle to Micro-A plug adapter. The carrier led group OMTP have recently endorsed micro-USB as the standard connector for data and power on mobile devices. [ [http://www.omtp.org/Publications/Display.aspx?Id=a9dd86d0-d9a6-4a47-81f8-4da8c402d1e7 OMTP Local Connectivity: Data Connectivity] at omtp.org]

Proprietary connectors and formats

Microsoft's original Xbox game console uses standard USB 1.1 signaling in its controllers and memory cards, but features proprietary connectors and ports. Similarly, IBM UltraPort uses standard USB signaling, but via a proprietary connection format. American Power Conversion uses USB signaling and HID device class on its uninterruptible power supplies using 10P10C connectors. HTC, a company which makes Windows Mobile-based Communicators, has a proprietary connector called HTC ExtUSB, which combines mini-USB with audio input and output. Nokia includes a USB connection as part of the Pop-Port connector on their mobile phones. The second-generation iPod Shuffle uses a TRS connector to carry USB, audio, or power signals. Many digital cameras have a tiny 8 pin connector that combines USB with video and audio out. There are at least 10 different types of non-standard Mini-USB receptacles and jacks currently in use. Because of this, the USB-IF created the Micro series of receptacles and jacks, so as to standardize on one jack that delivers both power and data.

USB cables

The maximum length of a standard USB cable is convert|5.0|m|ft|1|sp=us. The primary reason for this limit is the maximum allowed round-trip delay of about 1500 ns. If a USB device does not answer to host commands within the allowed time, the host considers the command to be lost. When adding up the USB device response time, delays from using the maximum number of hubs, and delays from the connecting cables, the maximum acceptable delay per cable turns out to be 26 ns. [ [http://www.usb.org/developers/usbfaq/#cab1 USB Frequently Asked Questions] at USB.org] The USB 2.0 specification requires cable delay to be less than 5.2 ns per meter (which is close to the maximum achievable speed for standard copper cable ^{[citation needed]} ). This allows for a 5 meter cable.

The data cables are a twisted pair to reduce noise and crosstalk.

Maximum Useful Distance

Although a single cable is limited to 5 meters, the USB specification permits up to five USB hubs in a long chain of cables and hubs. This allows for a maximum distance of 30 meters between host and device, using six 5-meter cables and five hubs. In actual use, since some USB devices have built-in cables for connecting to the hub, the maximum achievable distance is 25 meters + the length of the device's cable.

Since USB provides power for devices connected to the bus, a special type of USB extender cable was created, consisting of a miniature one-port USB hub molded onto one end of a 5-meter cable. These mini-hubs are fully self-contained within the cable, requiring no separate bulky hub device and no external power. They are as simple to use as plugging cables together, with each hub drawing power through all the previous single-port hubs in the chain. Because bus power is limited, the most practical arrangement consists of four single-port hub extender cables, one plain 5 meter cable and, at the very end, a powered multiport hub to support multiple USB devices.

Power

The USB specification provides a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. [cite web |title=“7.3.2 Bus Timing/Electrical Characteristics” |work=Universal Serial Bus Specification |url=http://www.usb.org/developers/docs/ |publisher=USB.org] There are two types of devices: low-power and high-power. Low-power devices draw 1 unit load, which is defined to be 100 mA. High-power devices draw 5 unit loads or 500 mA. All devices default as low-power but the devices software may request high-power as long as the power is available on the providing bus. [http://www.usb.org/developers/docs/]

A bus-powered hub is initialized at 1 unit load and transitions to 5 unit loads after hub configuration is obtained. Any device connected to the hub will draw 1 unit load regardless of the current draw of devices connected to other ports of the hub (i.e 1 device connected on a 4 port hub will only draw 1 unit load despite the fact that 5 unit loads are being supplied to the hub). [http://www.usb.org/developers/docs/]

A self-powered hub will supply 5 unit loads to any device connected to it. A battery powered hub may supply 1 or 5 unit loads. In addition, the V_BUS will supply 1 unit load upstream for communication if parts of the Hub are powered down. [http://www.usb.org/developers/docs/]

"On-The-Go" and "Battery Charging Specification" both add new powering modes to the USB specification. The latter specification allows USB devices to draw up to 1.5 A (low and full speed or 900mA in Hi-Speed mode) from hubs and hosts or up to 1.8A for dedicated chargers that follow the Battery Charging Specification. The dedicated charger shorts the D+ and D- pins together and will not send or receive any information on those lines, allowing for the creation of very simple, high current chargers to be manufactured. The increased current (faster charging) will occur once the host/hub and devices both support the new charging specification.

As of June 14, 2007, all new mobile phones applying for a license in China are required to use the USB port as a power port. [cite news |url=http://www.eetimes.com/rss/showArticle.jhtml?articleID=199800238&cid=RSSfeed_eetimes_newsRSS |title=China to enforce universal cell phone charger |publisher=EETimes.com|author=Cai Yan |date=2007-05-31 |accessdate=2007-08-25] [zh icon [http://www.dianyuan.com/bbs/u/63/2015571206841181.pdf The Chinese FCC's technical standard] ]

In September, 2007 the Open Mobile Terminal Platform—a forum dominated by mobile network operators but including manufacturers such as Nokia, Samsung, Motorola, Sony Ericsson and LG—announced that its members had agreed on micro-USB as the future common connector for mobile devices. [cite news |url=http://www.news.com/2100-1041_3-6209247.html |title=Pros seem to outdo cons in new phone charger standard |publisher=news.com |date=September 20, 2007 |accessdate=2007-11-26] [cite news |url=http://web.archive.org/web/20071220225110/www.omtp.org/news/news_pr_universal_cable.html |title=Press Release: Broad Manufacturer Agreement Gives Universal Phone Cable Green Light |publisher=OTMA |date=September 17, 2007 |accessdate=2007-11-26]

Non-standard devices

A number of USB devices require more power than is permitted by the specifications for a single port. This is a common requirement of external hard and optical disc drives and other devices with motors or lamps. Such devices can be used with an external power supply of adequate rating, which is allowed by the standard, or by means of a dual input USB cable, one input of which is used for power and data transfer, the other solely for power, which makes the device a non-standard USB device. Some external hubs may, in practice, supply more power to USB devices than required by the specification but a standard compliant device must not depend on this.

Some non-standard USB devices use the 5 V power supply without participating in a proper USB network. These are usually referred to as USB decorations. The typical example is a USB-powered reading light; fans, mug heaters (though some may include USB hubs [http://www.dealextreme.com/details.dx/sku.3195] ), battery chargers (particularly for mobile telephones), miniature vacuum cleaners, a miniature Lava Lamp, and even toy missile launchers are available. In most cases, these items contain no digitally based circuitry, and thus are not proper USB devices at all. This can theoretically cause problems with some computers — the USB specification requires that devices connect in a low-power mode (100 mA maximum) and state how much current they need, before switching, with the host's permission, into high-power mode.

In addition to limiting the total average power used by the device, the USB specification limits the inrush current (to charge decoupling and bulk capacitors) when the device is first connected; otherwise, connecting a device could cause glitches in the host's internal power. Also, USB devices are required to automatically enter ultra low-power suspend mode when the USB host is suspended; many USB hosts do not cut off the power supply to USB devices when they are suspended since resuming from the suspended state would become a lot more complicated if they did.

There are also devices at the host end that do not support negotiation, such as battery packs that can power USB powered devices; some provide power, while others pass through the data lines to a host PC. USB Power adapters convert utility power and/or power from a car's electrical system to run attached devices. Some of these devices can supply up to 1 A of current. Without negotiation, the powered USB device is unable to inquire if it is allowed to draw 100 mA, 500 mA, or 1 A.

The Apple SuperDrive uses a non-standard extension to USB to negotiate with the MacBook Air to draw 1.5 A from the USB port.Fact|date=October 2008 Due to the proprietary protocol, the SuperDrive only functions when connected directly to the Air, and cannot be operated with an external supply or through a USB hub, even if the hub can source the current specified on the package.Fact|date=September 2008

PoweredUSB

PoweredUSB uses standard USB signaling with the addition of extra power lines. It uses 4 additional pins to supply up to 6A at either 5V, 12V, or 24V (depending on keying) to peripheral devices. The wires and contacts on the USB portion have been upgraded to support higher current on the 5V line, as well. This is commonly used in retail systems and provides enough power to operate stationary barcode scanners, printers, pin pads, signature capture devices, etc. This standard was developed by IBM, NCR, and FCI/Berg. It is essentially two connectors stacked such that the bottom connector accepts a standard USB plug and the top connector takes a power connector.

USB compared with FireWire

USB was originally seen as a complement to FireWire (IEEE 1394), which was designed as a high-speed serial bus which could efficiently interconnect peripherals such as hard disks, audio interfaces, and video equipment. USB originally operated at a far lower data rate and used much simpler hardware, and was suitable for small peripherals such as keyboards and mice.

The most significant technical differences between FireWire and USB include the following:
* USB networks use a tiered-star topology, while FireWire networks use a repeater-based topology.
* USB uses a "speak-when-spoken-to" protocol; peripherals cannot communicate with the host unless the host specifically requests communication. A FireWire device can communicate with any other node at any time, subject to network conditions.
* A USB network relies on a single host at the top of the tree to control the network. In a FireWire network, any capable node can control the network.
* USB runs with a 5 V power line, whereas Firewire can supply up to 30 V.

These and other differences reflect the differing design goals of the two buses: USB was designed for simplicity and low cost, while FireWire was designed for high performance, particularly in time-sensitive applications such as audio and video. Although similar in theoretical maximum transfer rate, FireWire 400 tends to have the performance edge over USB 2.0 Hi-Speed in real-world uses, especially in high-bandwidth use such as external hard-drives. [cite web|url=http://www.cwol.com/firewire/firewire-vs-usb.htm |title=FireWire vs. USB 2.0 - Speed Tests |accessdate=2007-08-25] [cite web|url=http://www.digit-life.com/articles/usb20vsfirewire |title=USB 2.0 vs FireWire |publisher=Digit-Life |accessdate=2007-08-25] [cite web|url=http://www.pcmag.com/article2/0,4149,847716,00.asp |title=The Great Interface-Off: FireWire Vs. USB 2.0 |publisher=PC Magazine |accessdate=2007-08-25|last=Metz|first=Cade] [cite web|url=http://www.g4tv.com/techtvvault/features/39129/USB_20_Versus_FireWire_pg3.html |title=USB 2.0 Versus FireWire|accessdate=2007-04-26|author=Heron, Robert|publisher=TechTV |accessdate=2007-08-25] The newer FireWire 800 standard is twice as fast as FireWire 400 and outperforms USB 2.0 Hi-Speed both theoretically and practically. [cite web | url = http://www.usb-ware.com/firewire-vs-usb.htm | title = FireWire vs. USB 2.0 | publisher = USB Ware | accessdate = 2007-03-19 ] The chipset and drivers used to implement USB and Firewire have a crucial impact on how much of the bandwidth prescribed by the specification is achieved in the real world, along with compatibility with peripherals. [cite web|url=http://www.anandtech.com/mb/showdoc.aspx?i=2602&p=15 |title=Firewire and USB Performance |accessdate=2008-02-01|author=Key, Gary|date=2005-11-15] Audio peripherals in particular are affected by the USB driver implementation.Fact|date=July 2008

Initially, cost was significant in USB being more widespread than FireWire. Over time, USB benefited from network effect.

Version history

Prereleases

USB OTG Logo

* USB 0.7: Released in November 1994.
* USB 0.8: Released in December 1994.
* USB 0.9: Released in April 1995.
* USB 0.99: Released in August 1995.
* USB 1.0 Release Candidate: Released in November 1995.

USB 1.0

* USB 1.0: Released in January 1996.
Specified data rates of 1.5 Mbit/s ("Low-Speed") and 12 Mbit/s ("Full-Speed"). Did not anticipate or pass-through monitors. Few such devices actually made it to market.
* USB 1.1: Released in September 1998.
Fixed problems identified in 1.0, mostly relating to hubs. Earliest revision to be widely adopted.

USB 2.0

* USB 2.0: Released in April 2000.
Added higher maximum speed of 480 Mbit/s (now called "Hi-Speed"). Further modifications to the USB specification have been done via Engineering Change Notices (ECN). The most important of these ECNs are included into the USB 2.0 specification package available from [http://www.USB.org USB.org] :
** Mini-B Connector ECN: Released in October 2000.
Specifications for Mini-B plug and receptacle. These should not be confused with Micro-B plug and receptacle.
** Errata as of December 2000: Released in December 2000.
** Pull-up/Pull-down Resistors ECN: Released in May 2002.
** Errata as of May 2002: Released in May 2002.
** Interface Associations ECN: Released in May 2003.
New standard descriptor was added that allows multiple interfaces to be associated with a single device function.
** Rounded Chamfer ECN: Released in October 2003.
A recommended, compatible change to Mini-B plugs that results in longer lasting connectors.
** Unicode ECN: Released in February 2005.
This ECN specifies that strings are encoded using UTF-16LE. USB 2.0 did specify that Unicode is to be used but it did not specify the encoding.
** Inter-Chip USB Supplement: Released in March 2006.
** On-The-Go Supplement 1.3: Released in December 2006.
USB On-The-Go makes it possible for two USB devices to communicate with each other without requiring a separate USB host. In practice, one of the USB devices acts as a host for the other device.
** Battery Charging Specification 1.0: Released in March 2007.
Adds support for dedicated chargers (power supplies with USB connectors), host chargers (USB hosts that can act as chargers) and the No Dead Battery provision which allows devices to temporarily draw 100 mA current after they have been attached. If a USB device is connected to dedicated charger or host charger, maximum current drawn by the device may be as high as 1.5 A. (Note that this document is not distributed with USB 2.0 specification package.)
** Micro-USB Cables and Connectors Specification 1.01: Released in April 2007.
** Link Power Management Addendum ECN: Released in July 2007.
This adds a new power state between enabled and suspended states. Device in this state is not required to reduce its power consumption. However, switching between enabled and sleep states is much faster than switching between enabled and suspended states, which allows devices to sleep while idle.
** High-Speed Inter-Chip USB Electrical Specification Revision 1.0: Released in September 2007.

USB 3.0

On September 18, 2007, Pat Gelsinger demonstrated USB 3.0 at the Intel Developer Forum. USB 3.0 is targeted at ten times the current bitrate, reaching roughly 4.8 Gbit/s (600MB/s) by utilizing two additional high-speed differential pairs for "Superspeed" mode at a clock frequency of 2.5GHz , and with the possibility for optical interconnect.cite web |url=http://www.pcworld.com/article/137551/faster_usb_30_is_coming.html |title=Faster USB 3.0 Is Coming |accessdate=2008-07-04 |publisher=PC World |date=2007-09-24] [cite web |url=http://www.reghardware.co.uk/2008/01/09/ces_usb_3_revealed/ |title=Revealed: USB 3.0 jacks and sockets |accessdate=2008-01-22 |publisher=RegHardware.co.uk |date=2008-01-09 ] The two new differential pairs make the cable about as thick as an ethernet cable and provide full-duplex transfers.cite web |url=http://www.maximumpc.com/article/features/everything_you_need_know_about_usb_30_plus_first_spliced_cable_photos |title=Everything You Need to Know About USB 3.0, Plus First Spliced Cable Photos |accessdate=2008-08-22 |publisher=www.maximumpc.com |date=2008-08-18 ] The USB 3.0 specification was 90% complete as of August 13, 2008 [ [http://news.cnet.com/8301-13924_3-10016929-64.html Intel USB 3.0 update resolves dispute with Nvidia, AMD] ] and commercial products are expected to arrive in 2009 or 2010. [cite web |url=http://news.cnet.com/8301-10784_3-9780794-7.html |title=USB 3.0 brings optical connection in 2008 |accessdate=2008-07-04 |publisher=cnet.com |date=2007-09-18|first=Stephen |last=Shankland ] USB 3.0 is designed to be backwards-compatible with both USB 2.0 and USB 1.1 and employs more efficient protocols such as 8b/10b encoding cite web |url=http://www.tmworld.com/article/CA6599791.html?industryid=47184|title=USB 3.0 is coming|accessdate=2008-10-01|publisher=www.tmworld.com|date=2008-10-01 ] to conserve power while increasing the maximum power available for connected devices.

Related technologies

The PictBridge standard allows for interconnecting consumer imaging devices. It typically uses USB as the underlying communication layer.

The USB Implementers Forum is working on a wireless networking standard based on the USB protocol. Wireless USB is intended as a cable-replacement technology, and will use ultra-wideband wireless technology for data rates of up to 480 Mbit/s. Wireless USB is well suited to wireless connection of PC centric devices, just as Bluetooth is now widely used for mobile phone centric personal networks (at much lower data rates).

See also

Serial cable (Bidirectional Communication)
* Serial ATA
* RS-232
* Serial Null Modem Cable
* FireWire
* HP-IL
* Sync cable
* Enhanced mini-USB
* USB On-The-Go (master / slave)
* Ethernet over USB
* Wireless USB
* USB streaming
* HCI (UHCI, EHCI {xHCI 0.9 SuperSpeed - USB 3.0}, WHCI 1.0,)
* CEA-936-A
* U3
* [http://news.softpedia.com/news/USB-Graphics-Adapters-UGA-Delivered-to-Mass-Market-Retail-by-DisplayLink-and-EVGA-84870.shtml UGA] (USB Graphic Adapter)
* List of device bandwidths
** ACCESS.bus
** Apple Desktop Bus
* PS/2 connector
* DE-9 connector

External links

* [http://www.qimaging.com/support/downloads/documents/FirewireUSB.pdf Overview comparison between FW and USB]
* [http://www.usb.org/ Home of USB Implementers Forum, Inc.]
** [http://www.usb.org/developers/docs/ USB Specification]
* [http://developer.intel.com/technology/usb/uhci11d.htm Intel Universal Host Controller Interface (UHCI)]

USB 3.0

* [http://www.usb.org/usb30 USB Promoter Group - Mission Statement] at USB.org
* [http://arstechnica.com/news.ars/post/20070918-intel-announces-demonstrates-usb-3-0.html Intel announces, demonstrates USB 3.0] Ars Technica 2007-09-18
* [http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=201807389 USB 3.0 guns for Firewire] eeTimes 2007-09-18