Recognizing the general computing public's unquenchable greed for speed, a group of industry insiders banded together several years ago to develop a next-generation ATA specification that will provide not just faster speeds, but scalable performance for the next decade. This group is known as the Serial ATA Working Group, and today it has nearly 100 members including Intel, Seagate, Maxtor, Dell, and APT Technologies. Working Group members used the Intel Developer Forum to spread the word about Serial ATA and demonstrate its current feasibility and capabilities, as well as its promise for the future.
ATA is an interface for desktop system drives that is used to connect hard drives and other peripherals to a PC. First introduced in the mid-1980s, Parallel ATA has served the industry well, but it has just about reached its technical limits. Since its introduction, a new era of desktop storage has emerged; an era of larger and faster hard drives is pushing the boundaries of the Parallel ATA interface. There are new demanding applications for desktop drives that are screaming for a more flexible and creative way to attach new drives. The increased use of digital video in all realms is one obvious factor driving the demand for faster and better storage interfaces.
The spec that the Serial ATA Working Group has come up with to address these demands is known as Serial ATA 1.0, and it replaces the latest Parallel ATA technology, which is known as Ultra ATA/100. When one thinks of parallel versus serial, one usually envisions a parallel technology being able to move more bits than a serial technology, but in the case of Parallel ATA versus Serial ATA, it isn't quite that simple. Mark Hartney, director of technical marketing for Silicon Image, explains that while Serial ATA does move data in a single stream, it can do it faster than Parallel ATA does because it is not tied to a particular clock speed the way Parallel ATA is. Serial ATA wraps many bits of data into packets and then at a higher speed (30 times faster) than parallel, transfers the packets in a single stream (serially) down the wire to or from the host.
With first-generation speeds of 150MB/sec and the ability to achieve data transfer rates of 600MB/sec with future generations, the technology is scalable to maintain compatibility with future computer platform enhancements. Significant end-user benefits result from simpler configuration due to fewer jumper and setting requirements, allowing far easier upgradeability of storage devices. Developed as a drop-in solution, SATA is compatible with today's software (it is O/S-transparent) and runs on existing architectures without modification. SATA is also compatible with all ATA and ATAPI storage devices.
Serial ATA will be particularly popular with OEMs and system integrators due to improvements in cabling and connectors. The specification allows for thinner, more flexible cables, and lower pin counts, enabling simpler routing and installation; this improves thermal design and facilitates smaller form-factor systems. It also makes motherboard routing easier and uses smaller connectors than existing parallel ATA technology.
Demo #1: DVD+RW and ATAPI
Among the technical demonstrations at this year's Intel Developer Forum, one of the most interesting was the one conducted by Intel, Philips, and Silicon Image. This team demonstrated the broad applicability of Serial ATA with what they called "the world's first ATAPI device running on SATA." The demo consisted of a Philips DVD+RW, a Silicon Image SATALink PCI-to-SATA host controller, and a SATA device bridge on an Intel Pentium 4-based motherboard. The system recorded live video in real time directly onto a DVD+RW disc, which was then played on a commercial DVD player to verify compatibility and high-quality performance. The demo also featured Western Digital's Serial ATA hard disk drives and Mediostream's neoDVD video capture and authoring software.
Silicon Image's Mark Hartney notes that if you had a system like the one at the Forum, "you could use a DV camcorder to record real time to the disc, pop the disc out, and put it in a player and start editing." He calls the demonstration "dramatic" and says that the demo was purposely designed to put Serial ATA to the test. "Philips wanted to do something that would be really challenging," he says.
Hartney sums up the message of the demo as follows: "As the industry migrates to Serial ATA, optical drives will have to convert, too. This isn't just a standard for hard drives." Serial ATA will need to incorporate ATAPI command sets, he says, and this demonstration showed its feasibility. "It showed that ATAPI commands could be sent across the Serial ATA bus," he says. "It showed optical drive makers that you can do this today."
Hartney believes that the proliferation of video content is driving growth of the ATAPI-based optical drive market, including DVD+RW, DVD-ROM, CD-ROM and CD-R/RW devices. In fact, research conducted by Wolfgang Schlichting at market research firm IDC indicates that the optical drive market will surpass 200 million drives by 2004. Therefore, says Hartney, it is important to get this growing segment of the storage peripherals market on board the SATA bandwagon as quickly as possible, for the manufacturers' sake, the consumers' sake, and for the sake of the whole industry. Commenting on the demo back in September, Rae Cho, Silicon Image director of product marketing, storage semiconductors, noted, "There's no question that the market is aggressively moving to Serial ATA. Following the lead of their hard disk counterparts, we expect to see optical drive manufacturers incorporate Serial ATA into their products to ensure interoperability with the new SATA motherboards and add-in-cards that will begin proliferating the market this Fall." And he vowed that his company would have SATA 1.0 products available to expedite the mass migration.
Demo #2: Taking ATA to the Next Step (SATA II)
Another demo at the Intel Developer Forum was notable in that it addressed Serial ATA's evolutionary path into the future. At the Forum, Seagate, Intel, and Silicon Image demonstrated new Serial ATA II interface capabilities that are defined by the upcoming Serial ATA II specification. The Serial ATA Working Group obviously sees SATA as a work-in-progress that will be tweaked as we go along—always remaining backward-compatible, of course. "Serial ATA II adds features not fully implemented in ATA 1.0," says Seagate manager of I/O planning Marc Knoblitt.
While the Serial ATA 1.0 specification already ensures performance headroom for years to come, the Serial ATA II specification enhances Serial ATA with features that add data-handling intelligence to provide additional value for entry-level server, networked storage, and high-end PC markets. These features are expected to further increase the momentum of Serial ATA in these targeted applications and to help accelerate the industry transition from Parallel ATA to Serial ATA.
The working system showcased by Seagate, Intel, and Silicon Image at the Forum implemented Native Command Queuing—a key new capability defined in the Serial ATA II specification that enables intelligence data handling. The demonstration showed an integrated Serial ATA solution including a hard drive, host controller, and system software—all required to perform command queuing—and was the first real-world example of new features outlined in the Serial ATA II specification scheduled to be released next quarter. The demonstration represented an important step toward enabling a future of data-intensive and rich content delivered via PCs, consumer electronics devices, home network hubs, and ubiquitous small servers.
Native Command Queuing is perhaps the most anticipated feature of the new SATA II specification. It enables a hard drive to take multiple requests for data from the processor and rearrange the order of those requests to maximize throughput. Serial ATA II hard drives will be able to queue and execute requests without any assistance from a system's CPU or motherboard chipset.
The demo highlighted the benefits of the Serial ATA Native Command Queuing as prototyped by the three companies involved. The system used Silicon Image's SATALink SiI 3112A PCI to Serial ATA host controller, a custom prototype drive provided by Seagate and software developed by Intel. In a head-to-head comparison, the Seagate Serial ATA native queuing drive and an equivalent Parallel ATA drive were both exercised with a disc-intensive workload. The IOPS (I/Os per second) performed by each drive was displayed real-time on side-by-side "tachometers."
According to Seagate's Marc Noblitt, the demo "showed that Serial ATA II is working and feasible" and that it is "definitely another step forward." He says the tachometer test showed a 20-25 percent performance improvement over Parallel ATA. Knoblitt emphasizes, however, that speed isn't SATA's only advantage and not even its biggest. "It provides more intelligent ways to handle data," he says, and most importantly, "frees up the CPU." The main performance benefit is something you'll only see in the long run when because you have Serial ATA, your hard drive will not bottleneck your system's performance.
While the demonstration focused on Native Command Queuing, Serial ATA II has many other advantageous new features including: (1) Performance improvements, such as out-of-order execution/delivery and data scatter/gathering; (2) Complete enclosure management, including fan control, activity indicators, temperature control, new device notification; (3) Backplane interconnect solution to extend trace lengths beyond those allowed by Serial ATA 1.0 for use in racks of hot-swappable drives; and (4) Efficient connectivity to a large number of drives.
Commenting on the demo back in September, Parviz Khodi, Silicon Image vice president of marketing, stated, "Only integrated Serial ATA drive and host solutions have the features necessary to perform native command queuing, which is critical to Serial ATA II functionality. We designed the SiI 3112A host controller with enhanced capabilities beyond the requirements of the Serial ATA 1.0 specification, enabling the implementation and demonstration of next-generation Serial ATA II command queuing capability today."
Beginning next quarter, Serial ATA 1.0 will be deployed in numerous products to connect such internal storage devices as hard disks, DVDs, and CD-R/RW drives to the motherboard in desktop and mobile PCs, cost-sensitive servers, and networked storage. Serial ATA II products may become available as early as fourth quarter 2003, and will be fully compatible with Serial ATA 1.0 products and maintain software compatibility with today's operating systems.
Silicon Image's Mark Hartney observes that Serial ATA II may not be as readily adopted as version 1.0 because it will face competition from SCSI in the server market. "Serial ATA II and Serial Attached SCSI will co-exist," he says. "It will be a question of market percentage." He feels, however, that due to higher-volume production, the simpler and more universally supported SATA II will have a distinct cost advantage over any SCSI solution. But on the desktop, the success of Serial 1.0 will be a slam dunk. Says Noblitt, "Ultimately, the entire industry will drop Parallel ATA for Serial ATA."
More information about the Serial ATA and Serial ATA II working groups is available at www.serialata.org, www.siliconimage.com, and www.seagate.com.