USB 3.0 specification with SuperSpeed published
Version 3.0 of the Universal Serial Bus (USB), "more than ten times as fast as USB 2.0", was mentioned for the first time at the Intel developer forum (IDF) in autumn 2007, and the USB Implementers Forum led by Intel has now made the final version of the new specification available to download. The document, extending to around 480 pages and almost 3.5 MB, explains in particular the new SuperSpeed mode of operation, promised to allow data transfer at up to 300 MB/s. A USB 3.0 host adapter will still be compatible with the high-speed transfer mode introduced officially with USB 2.0 some eight years ago, which in theory goes up to 60 MB/s (480 Mbit/s), as well as the full-speed (12 Mbit/s) and low-speed (for keyboards and mice) operating modes already possible with USB 1.0/1.1. In contrast to the transition from USB 1.1 to USB 2.0, however, SuperSpeed mode requires new USB cables which, in addition to the existing pair of data lines (D+/D-), which only had to be implemented as an unshielded twisted pair (UTP), now use a separate shielded pair of conductors (shielded differential pair, SDP) for each direction of transfer, and a common shield covers the whole cable to give compliance with electromagnetic compatibility limit values.
USB 3.0 plugs will also have five additional contacts, while remaining compatible with existing USB sockets, because the new contacts have been squeezed into previously unused positions. But this doesn't work with Micro-USB connectors, which are being fitted with an extender. The optical connectors mentioned by Intel in 2007, though not contained in the specification, may be coming later, because the SuperSpeed protocol is designed to be independent of the physical connection medium.
USB 3.0 host controllers will probably not be found in Intel's Ibex Peak chipsets for desktop and notebook processors, expected in the second half of 2009 as part of the Nehalem generation, but PCI controller chips that can be retrofitted with a USB 3.0 adapter may well be: that's what happened in the early days of USB 2.0. Symwave will demonstrate its first SuperSpeed physical layer device at the SuperSpeed USB Developers Conference being held today and tomorrow in San Jose. The chipset makers AMD and Nvidia earlier complained that Intel was withholding information about an initial implementation of an extended host controller interface (xHCI) for SuperSpeed, but that has now apparently been rectified.
Modern chipsets and their southbridge i/o controller hubs contain a number of USB host controllers, typically a low-speed/full-speed controller (Intel/VIA: Universal HCI, UHCI, AMD-ATI/Nvidia: Open HCI, OHCI) for every two USB ports, often adding up to six of them, as well as one or two "extended" host controllers (Enhanced, EHCI) for high-speed connections. The USB root hubs that are also integrated into the chipset take data traffic to the correct host controller, depending on its type. In future they are also going to hold an xHCI controller.
The Personal Computer Memory Card International Association (PCMCIA) is also backing USB 3.0, specifically in its coming specification for ExpressCard 2.0 notebook expansion cards, also promised to support PCI Express 2.0.