USB 3.0 is the third major revision of the Universal Serial Bus (USB) standard for computer connectivity.

USB 3.0 has transmission speeds of up to 5 Gbit/s, which is 10 times faster than USB2.0 (480 Mbit/s). USB 3.0 significantly reduces the time required for data transmission, reduces power consumption, and is downward compatible with USB 2.0. The USB 3.0 Promoter Group announced on 17 November 2008 that the specification of version 3.0 had been completed and had made the transition to the USB Implementers Forum (USB-IF), the managing body of USB specifications. This move effectively opened the specification to hardware developers for implementation in future products.

Features:

A new feature is the "SuperSpeed" bus, which provides a fourth transfer mode at 5.0 Gbit/s. The raw throughput is 4 Gbit/s, and the specification considers it reasonable to achieve 3.2 Gbit/s (0.4 GB/s or 400 MB/s), or more, after protocol overhead

In order to achieve increased data throughput, USB 3.0 introduces an additional two differential pairs over which full-duplex signaling occurs. This results in a USB 3.0 cable having a total of 8 wires: one power, one ground, two for non-SuperSpeed data (as one differential pair), four wires for SuperSpeed data (as two differential pairs), and a shield that was 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. Standard-A plugs have been extended in length (accordingly the port is deeper) with the SuperSpeed pins extending beyond the legacy pins. SuperSpeed Standard-B plugs have the SuperSpeed pins placed on top of the existing form factor.

To ensure backwards compatibility (limited to legacy modes):

• A legacy Standard-A plug will fit a SuperSpeed Standard-A port;
• A legacy Standard-B plug will fit a SuperSpeed Standard-B port;
• A SuperSpeed Standard-A plug will fit a legacy Standard-A port;

However, a SuperSpeed Standard-B plug will not fit a legacy Standard-B port.

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-, device-, and function-level power management.

The bus power spec has been increased so that a unit load is 150 mA (+50% over minimum using USB 2.0). An unconfigured device can still draw only one unit load, but a configured device can draw up to six unit loads (900 mA, an 80% increase over USB 2.0 at a registered maximum of 500 mA). Minimum device operating voltage is dropped from 4.4 V to 4.0 V.

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. Although electronicdesign.com estimated cables will be limited to 3 m at SuperSpeed, cables which support SuperSpeed are already available up to 5 m long.