Hard Disk Command Queuing Goes Native in Seagate Drive

SAN JOSE, Calif.—Storage developers may get a look at a new hard disk technology here this week at the Intel Developer Forum. At the conference and expo, hard drive manufacturer Seagate Technology Ltd. will reportedly demonstrate a forthcoming mechanism incorporating "native command queuing."

Seagate, based in Scotts Valley, Calif., is expected to announce the Barracuda 7200.7, a two-platter, 7,200-RPM, 200-Gbyte hard drive with 8 Mbytes of cache, sources close to the company said. Shipments of the drive are also expected to begin in November. Seagate will demonstrate a Serial ATA implementation of the drive at the Intel Developer Forum.

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Command queuing, as its name suggests, allows commands to be queued up, read and reordered before the driver acts upon data. The technology was defined as early as the ATA-4 specification, with the host controller determining the order of the commands to process. Native command queuing, part of the Serial ATA specification, allows up to 32 instructions to be queued and reordered by the hard disk controller itself.

Meanwhile, Western Digital Corp. of Irvine, Calif., on Monday announced a new version of its Raptor 10,000-RPM disk drive, which uses the current version of command queuing left over from parallel ATA. The company will begin shipping this 10,000-RM Raptor drive this November, when the company will announce pricing.

Western Digitals 74-Gbyte drive boasts the Ultra/150 CQ technology in addition to Rotary Accelerometer Feed Forward (RAFF) technology, designed to compensate for the vibration hundreds of drives produce while spinning in a drive cage.

Seagates implementation of native command queuing marks the beginning of a transition to a new technology. However, there are many performance considerations when comparing drives above and beyond their command ordering, such as the rotation speed of the platters, processor speed and the amount of cache.

"Theyre both fairly similar in terms of what the drive does," said Mark Hartney, director of technical marketing with Silicon Image Inc., Sunnyvale, Calif., which provided components to both Western Digital and Seagate.

Native command queuing requires a drive with fully integrated electronics, which can be "a little more efficient" than the type of queuing WD implemented, Hartney said. Western Digitals queuing, which the company calls "WD Ultra/150 Command Queuing," uses a bridge chip, he said.

"The key difference between the two is the number of steps and the sequence of steps required for the queuing operation," said Knut Grimsrud, principal engineer on Intel Corp.s I/O Architecture and Performance team in the companys R&D department; and chair of the storage industrys Serial ATA Working Group. The minimal command overhead implicit in the native Serial ATA implementation was the reason Intel chose to endorse it, he said.