Hardware Reference
In-Depth Information
contains a set of registers that shadow the contents of the traditional device registers, re-
ferred to as the Shadow Register Block. All SATA devices behave like Device 0 devices.
Devices shall ignore the DEV bit in the Device/Head field of received Register FISs, and
it is the responsibility of the host adapter to gate transmission of Register FISs to devices,
as appropriate, based on the value of the DEV bit.”
This means the shadow register blocks are “fake” PATA registers, allowing all ATA com-
mands, modes, and so on to be emulated. SATA was designed to be fully software com-
patible with ATA/ATAPI-5, which is why a SATA drive can report in some ways as if it
were PATA or running in PATA modes, even though it isn't.
ATA Features
The ATA standards have gone a long way toward eliminating incompatibilities and prob-
lems with interfacing IDE drives to ISA/PCI bus systems. The ATA specifications define
the signals on the 40-pin connector, the functions and timings of these signals, cable spe-
cifications, and so on. The following section lists some of the elements and functions the
ATA specifications defines.
ATA Commands
One of the best features of the ATA interface is the enhanced command set. The ATA in-
terface was modeled after the WD1003 controller IBM used in the original AT system.
All ATA drives must support the original WD command set (eight commands) with no
exceptions, which is why ATA drives are so easy to install in systems today. All IBM-
compatiblesystemshavebuilt-inROMBIOSsupportfortheWD1003,sotheyessentially
support ATA as well.
InadditiontosupportingalltheWD1003commands,theATAspecificationaddednumer-
ous other commands to enhance performance and capabilities. These commands are an
optional part of the ATA interface, but several of them are used in most drives available
today and are important to the performance and use of ATA drives in general.
Perhaps the most important is the
IDENTIFY DRIVE
command. This command causes the
drivetotransmita512-byteblockofdatathatprovidesalldetailsaboutthedrive.Through
this command, any program (including the system BIOS) can find out exactly which type
of drive is connected, including the drive manufacturer, model number, operating para-
meters, and even serial number of the drive. Many modern BIOSs use this information to
automatically receive and enter the drive's parameters into Complementary Metal Oxide
Semiconductor(CMOS)memory,eliminatingtheneedfortheusertoentertheseparamet-
ers manually during system configuration. This arrangement helps prevent mistakes that
