Tagged Command Queuing (TCQ) is a technology built into certain ATA and SCSI hard drives. It allows the operating system to send multiple read and write requests to a hard drive. ATA TCQ is not identical in function to the more efficient native command queuing (NCQ) used by SATA drives. SCSI TCQ does not suffer from the same limitations as ATA TCQ.
Before TCQ, an operating system was only able to send one request at a time. In order to boost performance, the OS had to decide the order of the requests based on its own, possibly incorrect, idea of what the hard drive was doing (otherwise known as I/O Scheduling). With TCQ, the drive can make its own decisions about how to order the requests (and in turn relieve the operating system from having to do so). The result is that TCQ can improve the overall performance of a hard drive if it is implemented correctly.
Famous quotes containing the word command:
“But as some silly young men returning from France affect a broken English, to be thought perfect in the French language; so his Lordship, I think, to seem a perfect understander of the unintelligible language of the Schoolmen, pretends an ignorance of his mother-tongue. He talks here of command and counsel as if he were no Englishman, nor knew any difference between their significations.”
—Thomas Hobbes (1579–1688)