TCQ, RAID, SCSI, and SATA explained
 

Over the last few years, Western Digital has maintained a virtual vice-lock on the high-performance, high-capacity desktop and enthusiast markets. The venerable WD Caviar series has combined enviable speed and capacity with reasonable prices. However, aside from a relatively obscure, short-lived SCSI line, when it came to the lucrative enterprise arena the firm simply watched from a distance as titans such as Seagate, Maxtor, and Hitachi battled for market share.

A little over a year ago WD tested the enterprise waters with the introduction of the world's first 10,000 RPM ATA drive, the Raptor WD360GD. The Raptor paired SCSI-class mechanics with the new and relatively inexpensive Serial ATA interface in an attempt to undercut the rather hefty premiums that SCSI subsystems demanded. StorageReview's performance results, however, revealed that while the WD360GD delivered world-class single-user results, its multi-user performance remained unimpressive when contrasted with existing 10k RPM SCSI units.

The WD360GD lacked a key element that the SCSI world has enjoyed for years- tagged command queuing (TCQ), a feature that intelligently reorders requests to minimize actuator movement. In September of 2003, Western Digital announced the follow-up Raptor WD740GD, a second-generation unit that brought a host of improvements to the line. Though the doubling of the Raptor's capacity to 74 gigabytes is the most visible improvement, the most intriguing undoubtedly is the implementation of TCQ.

http://www.storagereview.com/article...0625TCQ_1.html