Serial ATA: hits & misses

Computer Technology Review, April, 2004 by Paul Griffith, Linus Wong

It was a rising star in data storage. The technology promised new data speeds for desktop and laptop PCs, pencil-thin cables and power-thrifty electrical designs that would spawn a generation of smaller, cooler-running systems, and a price point that would drive down the cost of storage in enterprise environments. Designed as a replacement for ATA, the technology would be widely used in home and office PCs and stood to replace the venerable SCSI in an increasing number of workstations and entry-level servers. Eventually, some pundits predicted, it would pack enough performance and reliability to displace SCSI as the mainstay for enterprise computing.

Today, nearly two years after the first Serial ATA products came to market, the technology is delivering on many of its promises, leaving others unfulfilled and raising high expectations for a generation of capabilities to come.

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What Gave Rise to Serial ATA?

Parallel ATA has been the industry standard for connecting hard drives and other devices in desktop and mobile computers for more than a decade due to the technology's connection simplicity, low implementation costs and growing performance. But increasingly complex board designs, growing signal-timing requirements and other technological challenges are preventing parallel ATA from keeping pace with rising desktop performance demands.

Enter Serial ATA, a technology designed chiefly for desktop systems as a replacement for ATA and to make smaller, faster computers possible. Serial ATA also was billed as a low-cost storage interconnect for workstations and entry-level servers that would deliver greater performance and reliability than ATA, ultimately offer connectivity for external storage and enable fan-out devices for greater scalability.

Serial ATA also promised higher levels of scalability and reliability through serial signal transmissions, a method that, unlike parallel ATA technology, would deliver full bandwidth to each storage device. The technology would also eliminate the need for master/slave jumpers on ATA devices to simplify installation.

When the Serial ATA blueprint was complete, the design called for a 10-year performance roadmap, compatibility with existing ATA software, a seamless transition path from ATA, and intent to target typical volume ATA applications. As a replacement for ATA, for example, Serial ATA would deliver more bandwidth to meet growing demand for higher performance gaming PCs.

Serial ATA also added a hot-plug capability that would allow IT managers to expand storage on the fly and deepen ATA's penetration into the workstation and entry-level server markets. However, this optional feature has not been widely implemented, so end users must first ensure both the Serial ATA controller and disk drive support hot plug, and that the proper hot-plug cabling and backplane are used to avoid potential disk drive damage.

Serial ATA's Success, Desktop Replacement for ATA

As a replacement for UDMA disk drives in desktop systems, Serial ATA has been a resounding success. The initial promoters of the technology built strong and increasing industry support by maintaining a consistent and well-defined charter. The standards process was private, controlled by five companies, but well managed and open to broad industry participation. Today, Intel's south-bridges include two Serial ATA ports, and disk drives are available at multiple capacity and price points. Vendors are delivering on the promise of task file register software compatibility, bringing backward compatibility of Serial ATA controllers to existing ATA drivers already embedded in commercial operating systems.

More desktop platforms are standardizing on Serial ATA as the primary disk storage interface and, at this juncture, a full transition from ATA to Serial ATA on the desktop is limited only by the availability of Serial ATA CD and DVD drives. Current CD-ROM and DVD drives--which use existing parallel ATA technology--remain in widespread use.

The original Serial ATA specification was never meant to meet the needs of the high-end server and networked storage markets. To control development costs, Serial ATA 1.0 was developed without enterprise-class capabilities such as an advanced storage management protocol, scalable bandwidth for large numbers of drives, broad command queuing, active dual-port capability, and support for simultaneous multi-initiator access required for clustered environments.

Desktop Drives in Enterprise Environments

As Serial ATA moved from laboratory to production in preparation for desktop deployments, a new class of data was rapidly growing: reference information. More small and mid-size businesses with modest IT budgets were digitizing information requiring bulk storage including e-mail, presentations, graphics and a variety of images including CAD/CAM drawings, medical X-rays and bank checks, increasing demand for low-cost storage and forcing these businesses to seek a cost-effective alternative to high-end disk drives for storage of this infrequently accessed data.