User Manual

Constellation.2 Serial ATA Product Manual, Rev. G 8
1.1 About the Serial ATA interface
The Serial ATA interface provides several advantages over the traditional (parallel) ATA interface. The primary advan-
tages include:
• Easy installation and configuration with true plug-and-play connectivity. It is not necessary to set any jumpers or
other configuration options.
• Thinner and more flexible cabling for improved enclosure airflow and ease of installation.
• Scalability to higher performance levels.
In addition, Serial ATA makes the transition from parallel ATA easy by providing legacy software support. Serial ATA
was designed to allow you to install a Serial ATA host adapter and Serial ATA disc drive in your current system and
expect all of your existing applications to work as normal.
The Serial ATA interface connects each disc drive in a point-to-point configuration with the Serial ATA host adapter.
There is no master/slave relationship with Serial ATA devices like there is with parallel ATA. If two drives are attached
on one Serial ATA host adapter, the host operating system views the two devices as if they were both “masters” on two
separate ports. This essentially means both drives behave as if they are Device 0 (master) devices.
Note. The host adapter may, optionally, emulate a master/slave environment to host software where two
devices on separate Serial ATA ports are represented to host software as a Device 0 (master) and Device 1
(slave) accessed at the same set of host bus addresses. A host adapter that emulates a master/slave envi
-
ronment manages two sets of shadow registers. This is not a typical Serial ATA environment.
The Serial ATA host adapter and drive share the function of emulating parallel ATA device behavior to provide back-
ward compatibility with existing host systems and software. The Command and Control Block registers, PIO and DMA
data transfers, resets, and interrupts are all emulated.
The Serial ATA host adapter contains a set of registers that shadow the contents of the traditional device registers,
referred to as the Shadow Register Block. All Serial ATA devices behave like Device 0 devices. For additional informa-
tion about how Serial ATA emulates parallel ATA, refer to the “Serial ATA: High Speed Serialized AT Attachment” speci-
fication. The specification can be downloaded from www.serialata.or
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