Feature in SATA-II: Native Command Queuing

[Iceman]

NCQ is the acronym for Native Command Queuing. NCQ is a feature of SATA-II. NCQ was not supported in SATA-I.

Without NCQ, commands are performed by the disk in the order in which they are received. If the commands are reads and writes of data scattered randomly across the disk, a lot of time can be wasted on long seeks (mechanically moving the head long distances) between successive read/write operations. This is particularly the case in a multi-tasking system where many tasks are accessing the disk and the disk is heavily fragmented.

With NCQ, SATA-II drives will use an algorithm to determine the most efficient order in which to perform the read/write operations. The algorithm will reduce or eliminate the long seeks. This will reduce the overall time spent on seeking, which is the slowest operation a disk can perform.

Read more details: What is NCQ

[joseph]

Thanks, ICE
Also if your harddisks got offline frequently with some seek errors (you can read these error message from s.m.a.r.t.), it's suggested to turn off NCQ.