A new major feature is the SuperSpeed bus, which increases the maximum transfer rate to 5.0 Gbit/s.USB 3.0 receptacles are compatible with USB 2.0 device plugs for the respective physical form factors. However, only USB 3.0 Standard-B receptacles can accept USB 3.0 Standard-B device plugs.
The protocol uses Dual-simplex, over four additional wires, differential signaling separate from USB 2.0 signaling (thus six wires total) to achieve the full Superspeed 5.0 Gbit/s.
The 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.
The bus power spec has been increased so that a unit load is 150mA (+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, an 80% increase 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, electronicdesign.com estimated cables will be limited to 3 m at full speed.
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.
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