USB 3.0 explained: How the next-generation USB will reach speeds of 4.8 Gbit/s
June 9, 2009
Scheduled to hit the consumer market in 2010, USB 3.0 — also known as SuperSpeed USB — will deliver a tenfold improvement in data transfer rates while retaining backward compatibility with previous versions and adding new features that will make this communication standard all the more essential to the average consumer. But, speed aside, what changes is the next version of this popular standard going to bring?
A (very) quick overview of the USB technology
Because it has to allow for communication between such a diverse array of devices, the specifications of the USB standard are extremely complex and deal with issues from the high (protocol and supporting software) to the very low (electrical) level, which would make an exhaustive explanation unpractical; it is, however, quite simple to understand on a functional level.
Just like with the Internet, communication between two or more devices via USB is packet-based, which means information always travels on a USB cable in the form of chunks of data of a predefined length (1,500 bytes) rather than as a mere stream of data. The packet header carries information on the destination address and control information which allow for the detection and correction of transmission errors, while the rest of the packet contains the actual data to be transferred.
In order for USB to work on a wide array of devices, USB 2.0 supports three different transfer speeds: Low-speed (1.5 Mbit/s), Full-Speed (12 Mbit/s), and High-Speed (480 Mbit/s) USB. When two devices decide to initiate a data transfer, the host — which acts as the control unit — initiates a polling mechanism to establish which is the highest speed that both ends support, and the transfer then takes places at that rate.
What is going to change with USB 3.0
USB 3.0 will add to the previous three a fourth speed, dubbed SuperSpeed (5 Gbit/s), that will allow for a tenfold improvement in the data transfer rate whenever both ends support it. In order to achieve this, a number of changes had to be made in terms of both the materials used and the internal structure of connectors: for instance, data in new USB 3.0 connectors will be driven by nine, rather than the previous four, wires. In order to guarantee the promised speeds, the maximum cable length will also have to be cut down from 5 to 3 meters to reduce attenuation.
On the consumer level, the main benefit will certainly be the improved speed. As USB-IF President and Chairman Jeff Ravencraft put it during a keynote speech in Tokyo earlier last month, the tremendous transfer rate provided by SuperSpeed will mean that it will be personal computer hard drives, rather than the USB standard, that act as the bottleneck with the next specification.
But there will be other, more subtle advantages as well, particularly on the architectural level: power efficiency will be greatly improved thanks to the introduction of an idle status; the need for polling will be eliminated thanks to a few protocol changes, which will in turn eliminate the time overhead needed by the host to establish the transfer rate to be used; and finally, USB 3.0 is also said to be highly scalable and ready for further transfer rate improvements in the next future.
According to the timeline proposed by Ravencraft, the initial deployment of USB 3.0 devices should start in mid 2009, while its industry deployment is scheduled to start in the first quarter of 2010. The Japanese NEC has released a statement saying it aims to produce its first USB 3.0 controller by the end of the month, initially priced at USD$15.
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