SAN JOSE, Calif. The widely used USB interface officially gets an upgrade to a version 3.0 Monday (Nov. 17) at a developers' conference here where a handful of companies are expected to announce product plans for the new spec with data rates that could hit 400 Mbytes/second.
USB 3.0 is capable of delivering at least 300 Mbytes/s of throughput at the application layer. It is backwards compatible with early versions of the spec, however it will require new cabling and connectors and is limited to distances of about three meters, down from five meters for today's USB products.
The 3.0 spec, also called SuperSpeed USB, is unique in several respects. It uses a five wire cable--two dedicated transmit and two receive wires and a ground wire—to implement full duplex links at up to 5 Gbits/s each way at the physical layer. Previously USB used a two-wire, half-duplex architecture.
The external appearance of the Type-A connector is unchanged, but internally it has five new pins to support full duplex operation. The new connector fits in existing slots.
In rough terms, client USB 3.0 chips could require twice the number of gates and consume three times the power of today's USB chips, according to John O'Neill, vice president of marketing at Symwave, one of the companies demonstrating a USB 3.0 chip at the event.
However, thanks to its high data rates, USB 3.0 exceeds previous generations in terms of milliwatts per Gbit transferred, he said. "Additionally, because of the improved protocol, the host burden [in] processor cycles will be reduced and therefore the overall system power garners even more of an advantage on a mW/Gbit basis," he added.
Indeed, version 3.0 reduces traffic on the wire, in part to reduce power consumption. It adopts an interrupt driven protocol, rather than the previous polling approach. In addition communicates via point-to-point links rather than broadcasting data to all connected devices.
The spec also boosts the amount of power carried over the link from 500 to 900 milliamps to more rapidly charge devices via USB. It can now sense a connected devoice with a dead battery and deliver a trickle charge to enable the device to come back to life and establish a connection.
The spec is available as a download
for those willing to sign a USB adopter's agreement.