More HD Performance For Free: Command Queuing
While tagged command queuing is a standard feature for SCSI components, it has not been very successful in the ATA world. IBM was the only manufacturer that introduced a modified version of tagged command queuing into their DeskStar 75 GXP series. Unfortunately, controller support for TCQ was very limited and retarded its success.
Today, more and more SATA drives are going to support command queuing. It's tagged command queuing for all models that work with a parallel ATA interface plus SATA bridge, while all native SATA drives should be able to do native command queuing until the end of this year.
The secret behind command queuing is simple: Provided that the controller, the driver and the drive support command queuing, the latter is given the freedom to reorder incoming commands in a manner that helps to reduce rotational latency and to increase efficiency. As only the drive really knows where exactly some sectors that altogether add up to a document file are stored, it needs to determine the fastest way of retrieving them.
Command Queuing Hard Drives
Maxtor will launch their MaXLine III (on the right) with native Serial ATA on June 21. Intel provided two of these with every reviewer's kit.
Although command queuing has been under discussion for quite some time, it has not made it into the SATA 1.0 specification. Nevertheless Seagate is an early adopter of NCQ (native command queuing) while Western Digital introduced tagged command queuing (TCQ) with their WD740 Raptor. Maxtor is going to introduce their MaXLine III series that feature both native Serial ATA and NCQ.
Again, you can refer to our benchmark section, for our command queuing benchmarks.
Bridged SATA drives use converter chips, here it is a Marvell bridge on a MaXLine II 250 GB drive.
The MaXLine III comes with a native Serial ATA controller that also is capable of command queuing.
We received a prototype of Seagate's Barracuda 7200.7 with Native Command Queuing enabled in January already.