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Hewlett-Packard, Seagate and Adaptec demonstrated prototype versions of Serial Attached SCSI ( ) at the here this week. The companies, combined with a , are betting that the technology will stay a step ahead of a lower-end but increasingly powerful standard, Serial ATA ( ).
SATA has its roots in ATA, the technology used to plug hard drives into desktop computers. SAS, on the other hand, is the sequel for SCSI drives that's used for jobs such as servers, for which every whit of performance matters.
"Will SATA encroach? Yes," said Linus Wong, director of strategic marketing for Adaptec, which makes adapters that let computers control storage systems that are made of groups of hard drives. "People continue to push ATA to its limits...But at the end of the day, the requirement for SCSI is still there."
Adaptec is backing both technologies. SATA will be useful for accessing infrequently used data such as a bank's scanned image of a check, whereas SAS will be adopted for demanding server tasks such as databases with a heavy transaction rate, Wong said.
Prototype SAS controllers from Adaptec are scheduled to arrive late this year, with products going to server companies such as HP in early 2004 and general shipping starting in mid-2004, Wong said.
SATA and SAS are both examples of a newer technology that's remaking computer innards in which carefully synchronized data is transferred through a small number of high-speed "serial" wires instead of a large number of "parallel" wires. Other examples of serial technology include the IEEE 1394 and USB plug-in ports, along with the.
One secondary advantage of serial technologies is that thin cables replace broad "ribbon" cables, which often obstruct airflow inside computer cabinets. SAS and SATA use the same cables, though SAS can accept 8-meter lengths; SATA can accept only 1-meter lengths.
SATA, which is on the cusp of arriving in mainstream PCs, has encroached on SCSI's turf. For example, it brings to ATA drives "command queueing" technology, which lets a drive store up a burst of several commands. SCSI has a more sophisticated version, Wong said.
SATA also has fast, 1.5 gigabit-per-second transfer rates. SAS will leapfrog to 3gbps. Though SATA 2.0 is expected to match that speed not long after, a revamp of SAS to 6gpbs is also planned.
Tolerance for vibration is another difference--and one that becomes important when many drives are whirring simultaneously in the same cabinet, Wong said. Vibrations knock ATA drive components out of alignment, slowing performance, but SCSI drives can withstand more motion.
The SAS standard isn't quite final, but the T10 group of the International Committee for Information Technology Standards is expected to finish it in August or September, Wong said.