USB 3.0

In information technology, Universal Serial Bus (USB) is a serial bus standard to connect devices to a host computer. USB was designed to allow many peripherals to be connected using a single standardized interface socket and to improve 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, eliminating the need for an external power supply; and allowing many devices to be used without requiring manufacturer-specific device drivers to be installed.

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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, Microsoft and NEC.

Features

• A new major feature is the SuperSpeed bus, which provides a fourth transfer mode at 5 Gbit/s. The raw throughput is 500 MByte/s, and the specification considers it reasonable to achieve 400 MByte/s or more after protocol overhead.
• When operating in SuperSpeed mode, full-duplex signaling occurs over 2 differential pairs separate from the non-SuperSpeed differential pair. This results in USB 3.0 cables containing 2 wires for power and ground, 2 wires for non-SuperSpeed data, and 4 wires for SuperSpeed data, and a shield (not required in previous specifications).
• To accommodate the additional pins for SuperSpeed mode, the physical form factors for USB 3.0 plugs and receptacles have been modified from those used in previous versions. Standard-A cables have extended heads where the SuperSpeed connectors extend beyond and slightly above the legacy connectors. Similarly, the Standard-A receptacle is deeper to accept these new connectors. A legacy Standard-A cable will operate as intended and will never interact with the SuperSpeed connectors, ensuring backward compatibility. The Standard-B modifications could not be made as elegantly; the SuperSpeed connectors had to be placed on top of the existing form factor, making legacy Standard-B plugs workable on SuperSpeed Standard-B receptacles, but not vice versa.
• SuperSpeed establishes a communications pipe between the host and each device, in a host-directed protocol. In contrast, USB 2.0 broadcasts packet traffic to all devices.
• USB 3.0 extends the bulk transfer type in SuperSpeed with Streams. This extension allows a host and device to create and transfer multiple streams of data through a single bulk pipe.
• New power management features include support of idle, sleep and suspend states, as well as Link-, De vice-, and Function-level power management.
• The bus power spec has been increased so that a unit load is 150mA (+50% over minimum using USB 2.0). An unconfigured device can still draw only 1 unit load, but a configured device can draw up to 6 unit loads (900mA, an 80% increase over USB 2.0 at a registered maximum of 500mA). Minimum device operating voltage is dropped from 4.4V to 4V.
• USB 3.0 does not define cable assembly lengths, except that it can be of any length as long as it meets all the requirements defined in the specification. However, electronicdesign.com estimates cables will be limited to 3 m at SuperSpeed.
• Technology is similar to a single channel (1x) of PCI Express 2.0 (5-Gbit/s). It uses 8B10B encoding, line ar feedback shift register (LFSR) scrambling for data, spread spectrum. It forces receivers to use low frequency periodic signaling (LFPS), dynamic equalization, and training sequences to ensure fast signal locking.

Availability

Consumer products are expected to become available in 2010. Commercial controllers are expected to enter into volume production no later than the first quarter of 2010.NEC is aiming to produce its first USB 3.0 controller in June 2009, initially priced at US$15.00. Monthly production of NEC Electronics' µPD720200 host controller is expected to reach approximately 1,000,000 units in September 2009.

Windows 7 drivers are under development but no public releases have been made available as of June 2009. The Linux kern

el will support USB 3.0 with version 2.6.31, which will be released around August 2009.