EW31244SL7QV Datasheet, PDF (63/252 Pages) Intel Corporation – Intel® 31244 PCI-X to Serial ATA Controller

Intel^® 31244 PCI-X to Serial ATA Controller
Functional Blocks
4.2.5
Serial ATA II Native Command Queuing
Serial ATA II Command Queuing enables a hard drive to accept multiple commands from the
GD31244 controller and rearrange the completion order of those commands to maximize
throughput. The major portion of the drive’s command service time is seek and rotational delay for
the drive head to land on the appropriate data to transfer. The drive can use rotational optimizations
to select the next command to complete such that the major components of the service time, seek
and rotational delay, are minimized. A major advantage to command queuing is that the command
issue and completion overhead may be overlapped with the drive seek and rotational delay for a
different command's data transfer. For example, while a new command is being issued to the drive,
the drive may be seeking to locate the appropriate track on disk for data for a different command.
In essence, the latency for issuing the new command is saved since it was overlapped with the seek
for another command.
Serial ATA II Native Command Queuing provides an efficient and streamlined data transfer and
status return mechanism. This performance and efficiency is achieved through features of the
SATA II Native Command Queuing protocol that include race-free status return mechanism,
interrupt aggregation, and First Party DMA.
Developer’s Manual
April 2004
63