USB SuperSpeed Interesting Facts
There was a recent USB developers conference held at the Doubletree Hotel in San Jose, California on November 17-18, on SuperSpeed USB or USB 3. There was an estimated 1500 attendees: a sign of great amount of interested in the new standard which is not expected to show up for another year. Here is a post summarizing some of what I had been about to gather from various postings on the Web.
The huge feature of USB 3 is of course “SuperSpeed” which is a 5Gb/s transfer mode, “10x” as fast as the current 480Mb/s high speed mode that we have now. But, there is some thought to future expansion. This new protocol allows expansion and the links will negotiate to the highest speed supported. Currently 5Gb/s is the only specified speed.
It looks like the first devices will start to show up in 2010 and they will likely be mass storage. There are no chip sets out yet. There are some vendors with IP (Intellectual Property) to be used in custom designs. The first release of Windows 7 will not have SuperSpeed built in and Microsoft has not set plans to implement it yet. Also Apple is said to be studying the issue. One of the main goals of the standard is to require no host device-driver changes to support SuperSpeed.
How is this greatly enhanced speed accomplished with as much backward compatibility as possible? SuperSpeed traffic can travel in both directions at once (dual simplex). A USB 3 system will basically run a SuperSpeed bus and a USB 2 bus in parallel. The bus has two new shielded twisted pairs to run the SuperSpeed and still has the old unshielded twisted pair USB 2 data pair. Going to these two pairs enables not only simplified bus drivers which don’t have to turn around direction, but also more efficient usage as data can be flowing in both directions at once. You can see that the design of hubs are now twice as complicated as they now have to cope with two parallel, separate busses running through them. Hubs now have extra work to do as SuperSpeed is now really routed through the hubs, not using broadcasts as with USB 2. Of course the USB 2 part of a hub should work as its unchanged from current specs.
Another big thing is better power management. Now high power can use 900 mA and low power, 150 mA. The spec is power management, a lot of effort was put into building power management into all the protocol levels. The main thing here is laptops particularly are able to save power when devices are attached. An attached device doesn’t gain much by power managing, except it is really helping the host. If attached at SuperSpeed a device can now draw 150mA unconfigured and 900mA configured. Quite an amount of current.
Related posts:
