Unwilling to revisit the confusion surrounding the multiple host controller interface specs of Universal Serial Bus 1.0, Intel developed the new spec in conjunction with NEC, Philips, Lucent, Microsoft and Compaq. "On the second version of USB, we looked at how we could learn from the first round, and we decided that it was better for the industry for there to be one spec that was available to everybody," Jason Ziller, an Intel technology initiatives manager, said in releasing 2.0 this week.

When 1.0 was being developed, Intel evolved its own host controller spec, dubbed the universal host controller interface, and retained the rights. That prompted others in the industry to develop the open host-controller interface (OHCI) spec. But two specs only frustrated OS vendors charged with developing software support for multiple implementations of host controllers.

"The biggest difficulty . . . was that the software drivers developed for the host controllers had to be somewhat different to support each type," Ziller said.

The problem of multiple specs also surfaced when it came time for product validation and testing. Nathan Brookwood, president of market-research firm Insight64 (Saratoga, Calif.), said, "When 1.0 was being developed, Intel basically said, 'What happens on the bus is open, but what goes on in the host is proprietary.' Everybody else banded together and came up with an alternative."

He said the two specs "looked pretty much the same on the wire, but because of their differences, it made the whole validity testing and interoperability testing a lot more complicated."

The 2.0 enhanced host controller interface (EHCI) spec defines an architecture fully compatible with 1.1 and 2.0 devices and hubs. It can run 1.1 devices with existing 1.1 software drivers. The architecture is also more hardware-intensive, but consumes minimum CPU overhead, perhaps to avoid the software complexity that has, in part, stalled the rollout of IEEE's 1394 Firewire interface.

"The OHCI is a little more hardware-intensive, so we opted to make the EHCI a little more hardware intensive," Ziller said. "It's more efficient, ultimately. Since USB 2.0 is a high-speed interface, people ask 'Do you need a certain high-speed CPU to run it?' The answer is no."

Analysts believe that will also ease adoption rates. "Anything you could do to make the hardware do more ultimately helps facilitate industry acceptance," Brookwood said. "And the rollout is pretty much on target for early 2001."

Road to mass deployment

Initial support will come in the form of add-in cards, using a host controller from the likes of NEC or Lucent. "But you won't see mass deployment until it makes it into chip sets," Brookwood said, "and that won't be until the third quarter of 2001." High-speed scanners and storage devices, products drastically limited by the bandwidth of USB 1.0, look to be the first devices rolled out.

Market research firm Cahners In-Stat Group estimates that by 2004, about 750 million USB-equipped desktop and notebook PCs will be in use. Until ubiquity, most PC OEMs will offer at least a few models with USB 2.0, based on a motherboard with a discrete host or an add-in PCI board, In-Stat said. This bridge presents an opportunity for component manufacturers like Lucent, NEC and Philips to sell millions of host controllers.

Intel said that more than 25 companies have already licensed the spec, with an initial test suite expected in the first half of next year.

The spec looks to make memory access more efficient, decreasing the average number of memory accesses required to execute a USB transaction. Each data structure is optimized to describe large client data buffers, minimizing the memory footprint and amount of memory overhead.

The spec also looks to minimize hardware complexity. It presents a simple, asynchronous interface for software to provide the host controller with parameterized work items that the controller uses to execute transactions on USB. The interface allows software to asynchronously add work to the interface while the host controller is executing, without any synchronization required. The interface supports a simple hardware scatter/gather method for all interface data structures.

The new spec also includes optional interface extensions that support up to 64-bits of addressable memory space.