Seagate Mobile HDD Product Manual, Rev. A
7
1.1
About the Serial ATA Interface
The Serial ATA interface provides several advantages over the traditional (parallel) ATA interface. The primary advantages 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 users to
install a Serial ATA host adapter and Serial ATA disk drive in the current system and expect all of the existing applications to work as normal.
The Serial ATA interface connects each disk 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.
The Serial ATA host adapter and drive share the function of emulating parallel ATA device behavior to provide backward 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 information about how Serial ATA emulates parallel ATA, refer to
the
Serial ATA International Organization: Serial ATA
(Revision 2.6). The specification can be downloaded from
www.serialata.org
.
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 environment manages two sets of shadow registers. This is not a typical Serial ATA environment.
