The charter of the Serial Bus Protocol-3 Working Group — which includes Apple Computer Inc., Sony Corp., Matsushita Electric Industrial Co. and storage vendors Maxtor and Seagate — is to add native isochronous service support to serial bus protocols. When completed in the next six to 12 months, SBP-3 is expected to trigger demand for 1394-based hybrid hard disk drives that would reconcile the storage of computer data on PC hard drives with the use of the audio/video hard disk drive (AV-HDD) for time-shifting TV programs.

"Consumer electronics vendors have their hearts set on 1394 — a peer-to-peer, nonsupervised bus," observed David Wooten, chief technology officer for the Interface Products Division at Cypress Semiconductor. "USB wasn't designed for consumer electronics; the CE companies know that they can't count on a PC every time two random devices need to be connected."

The protocol "will simplify the market, and it makes the reasons for a 1394-based drive more obvious," said Michael Teener, chief technology officer at Zayante Inc. (Scotts Valley, Calif.).

Manufacturers would be able to build standalone 1394-based storage devices that "could sit on a desk or TV, housed in a PC or stored in a closet as a home server" and efficiently store both movies and data files, regardless of the source and the intended playback medium, said Peter Johansson, project leader for the SBP-3 group and a consultant at Congruent Software Inc. (Berkeley, Calif.).

Scott Smyers, vice president at Sony's Interconnect Architecture Lab, called the emerging SBP-3 standard "a natural evolution." The notion of adding isochronous support to serial bus protocols is not new, Smyers said: "We worked on the issue a few years ago when we were developing SBP-2."

But while the concept may not be new, the market still may not be ready for a hybrid drive, some analysts said.

Most combination products end up as niche offerings on the consumer market, because the technologies and functions necessary for each application tend to evolve at different speeds, and resolving the issues in converged devices is a tortuous process, said Jim Porter, president of Disk/Trend Inc. (Mountain View, Calif.).

Today, of 200 million hard drives, 75 percent are used for desktop PCs and the rest for notebooks and servers. Sales volumes for the so-called AV-HDDs are only in the couple of hundred thousands, Porter said, and sales of 1394-based drives also remain "negligible."

But once such copy-protected materials as Hollywood movies become broadly available on 1394-based devices, "the need for SBP-3 will soar, big time," said Johansson of the working group, which operates under NCITS' T-10 technical committee.

SBP-2, a transport protocol defined in 1999 for IEEE 1394, is essential to printers, scanners, DVD players and other devices, since it defines standard ways of encapsulating device commands, such as SCSI commands, over 1394. Isochronous data support was contemplated for SBP-2 but was eventually voted out of the final SBP-2 spec, Johansson said, because the "drive vendors got cold feet."

The isochronous debate "was ahead of its time, and there wasn't enough time to consider all the options," concurred Cypress' Wooten. Indeed, no real isochronous applications existed for disk drives at the time. Products like TiVo or the Replay AV-HDD didn't reach the market until 1999.

SBP-3 will pick up where its predecessor left off. Three key factors prompted the SBP-3 effort, Johansson said. "First, we wanted to develop methods to reduce the startup latency of disk drives from an idle condition." Second, the group saw the need to enable SBP-3-based devices to interoperate across one or more bridges specified as p1394.1 high-performance serial bus bridges.

Adding bridge awareness to the serial bus protocols is essential to home network applications," said Johansson.

Third, the industry sees native isochronous support not only as an obvious next step but also as crucial for vendors planning to build standards-based 1394 disk-drive appliances catering to both audio/video and computer functions.

Zayante's Teener believes the the SBP-3 standard will be implemented in phases. A "fast start" feature, designed to minimize drive startup latencies, has been well-received within the SBP-3 working group, having sparked "very little controversy," Teener said. It will be possible by yearend to enhance SBP-2 drives by adding the fast-start option, he said.

Isochronous support will come later, most likely next year, Teener said. Given the wealth of ways to optimize isochronous data in SBP drives, "we could get easily stuck in details."

Matters will get even more complicated when SBP-based drives are expected to handle multiple streams for read and write. "There is a lot of room for different buffer management, and in some cases, some patents already exist," he said. Teener predicts "a big war of performance" and expects some debate over how best to gauge performance when dealing with both isochronous and asynchronous data.

The working group must find a way to standardize "the format of isochronous data with time stamp information," Teener said.

Most sources acknowledged that those who developed AV-HDD over the past two years have already done substantial pioneering work. Their engineering efforts have yielded schemes for tuning acoustic features, managing multiple uninterrupted streams simultaneously, and developing appropriate error and recovery algorithms for both isochronous and asynchronous data.

Sony worked with Quantum and Western Digital, respectively, on AV-HDD prototypes in the past, but the consumer electronics giant has never commercialized either model.

Today's AV-HDD storage devices generally don't cope well with asynchronous data, Johansson said.

The AV-HDD, using the AV/C protocol, is designed to record streaming media in real-time: It takes the drive two hours, for example, to record a two-hour movie. With SBP-3, however, a drive could record the full movie in one asynchronous swoop. "You can record your movie as fast as your transmission pipe, be it DSL or cable modem," said Johansson.

Further, because AV-HDD is designed to function as an embedded file system, without using a host computer, it forces "a painfully slow way of setting up protocols and doing handshaking" before it starts storing asynchronous data, said Cypress' Wooten.

On the other hand, when a PC hard drive is used to store streaming media, the PC usually needs to throw away "much more processing power and bandwidth" to accommodate isochronous data, Johansson of the SP-3 group said. "It's just not efficient."

Sony's Smyers acknowledged that his company, through its projects with U.S. drive vendors, has gained some experience in blending protocols for handling asynchronous and isochronous data in a single drive. But "the stuff we developed in those prototypes was still very crude," he said.

When the SBP-3 protocol standard is completed, a consumer could, for example, transfer a home movie directly from a digital video camcorder to an external 1394-based hard drive without going through a computer. The computer, freed from the task of downloading the entire home movie onto its own hard drive, could directly interface with the external 1394 drive to edit the home movie by randomly accessing different parts of the movie asynchronously. The edited version could be played back directly on a TV or PC display as an isochronous stream — again, without having the signal go through the computer.

The SBP-3 standard is also expected to free drive manufacturers from the need to partition a hard drive for computer applications and AV purposes. Under the current environment, 1394 storage devices require support for two access protocols: SBP-2 (supporting asynchronous data), with reduced block commands (RBSs), and the AV/C protocol (for isochronous applications), with hard disk drive subunit commands. A hard drive supporting both protocols must partition the total storage area into two distinct components — RBC and AV/C — since neither protocol has knowledge of or access to the other protocol's partition.

An external 1394 drive exposes that partitioning problem plainly to drive vendors, because there is no way to control whether the device will be used primarily for computer storage or for A/V purposes.

The SBP-3 protocol standard could similarly be applied to optical storage devices, such as DVD drives. A DVD-ROM could leverage SBP-3 to become a DVD player, without depending on a PC to prevent the DVD-ROM drive from dropping frames.