USB 3.0
The SuperSpeed USB Logo
The USB 3.0 Icon
On September 18, 2007, Pat Gelsinger demonstrated USB 3.0 at the Intel Developer Forum. The USB 3.0 Promoter Group announced on November 17, 2008, that version 3.0 of the specification had been completed and was transitioned to the USB Implementers Forum (USB-IF), the managing body of USB specifications.[46] This move effectively opened the spec to hardware developers for implementation in future products. The first USB 3.0 ports were featured on the Asus P6X58 motherboard; however this board was canceled before production.[47]
[edit] Features
* A new major feature is the SuperSpeed bus, which provides a fourth transfer mode at 4.8 Gbit/s. The raw throughput is 4 Gbit/s, and the specification considers it reasonable to achieve 3.2 Gbit/s (0.4 GByte/s or 400 MByte/s) or more after protocol overhead.[48]
* 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).[49]
* 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. On the other end, the SuperSpeed Standard-B connectors are placed on top of the existing form factor. A legacy standard A-to-B cable will work as designed and will never contact any of the SuperSpeed connectors, ensuring backward compatibility. SuperSpeed standard A plugs will fit legacy A receptacles but SuperSpeed standard B plugs will not fit into legacy standard B receptacles (so a new cable can be used to connect a new device to an old host but not to connect a new host to an old device; for that, a legacy standard A-to-B cable will be required) [50]
* 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 1 unit load, but a configured device can draw up to 6 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 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. However, electronicdesign.com estimates cables will be limited to 3 m at SuperSpeed.[28]
* Technology is similar to a single channel (1x) of PCI Express 2.0 (5-Gbit/s). It uses 8B/10B encoding, linear feedback shift register (LFSR) scrambling for data and spread spectrum. It forces receivers to use low frequency periodic signaling (LFPS), dynamic equalization, and training sequences to ensure fast signal locking.
