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Sabtu, 06 Desember 2008

USB 3.0

On September 18, 2007, Pat Gelsinger demonstrated USB 3.0 at the Intel Developer Forum. The USB 3.0 Promoter Group announced on 2008-11-17 that version 1.0 of the specification has been completed and is transitioned to the USB Implementers Forum (USB-IF), the managing body of USB specifications. This move effectively opens the spec to hardware developers for implementation in future products.

A new major feature is SuperSpeed bus, which increases a maximum transfer rate to 4.8 Gbit/s.

USB 3.0 receptacles are compatible with USB 2.0 device plugs for the respective physical form factors. However, only USB 2.0 Standard-A receptacles can accept USB 3.0 Standard-A device plugs.

SuperSpeed protocols are supported via 4 extra wires for dedicated SuperSpeed transfers.

Protocol supports full-duplex data transfers. In addition, data transaction is based on asynchronous traffic flow with explicitly routed packet traffic, instead of the polled broadcast packet traffic in USB 2.0. A streams mode is added for bulk transfer mode. SuperSpeed protocol also supports continuous burst transfers.

New power management features include support of idle, sleep and suspend states, as well as link and function-level power management.

Maximum bus power is increased to 150mA per unit load (+50% over 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, 80% over USB 2.0). 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, estimated cables will be limited to 3 m at full speed.

The technology is similar to PCI Express 2.0 (5-Gbit/s). It uses 8B10B encoding, linear 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.


USB 3.0 devices supporting SuperSpeed bus are expected to be available in commercial controllers in the second half of 2009. Consumer products are expected to become available in 2010.

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