Hardware Reference
In-Depth Information
This means the shadow register blocks are “fake” PATA registers, allowing all ATA commands,
modes, and so on to be emulated. SATA was designed to be fully software compatible 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 problems with
interfacing SATA and PATA drives to systems. The ATA specifications define the signals on the
cables and connectors, the functions and timings of these signals, the cable specifications, the
supported commands, the features, and so on. The following section lists some of the elements and
functions the ATA specifications define.
ATA Commands
One of the best features of the ATA interface is the enhanced command set. The ATA command
interface 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-compatible systems have built-in
ROM BIOS support for the WD1003, so they essentially support ATA as well.
In addition to supporting all the WD1003 commands, the ATA specification added numerous 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 DEVICE
command. This command causes the drive to
transmit a 512-byte block of data that provides all details about the drive. 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 parameters, 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, eliminating the need for the user
to enter these parameters manually during system configuration. This arrangement helps prevent
mistakes that can later lead to data loss when the user no longer remembers what parameters he used
during setup.
The
Identify Device
data can tell you many things about your drive, including the following:
• Whether the drive has rotating media (and if so, how fast), or whether it is a solid-state drive
(SSD) instead
• Whether the
TRIM
command is supported (or not) on SSDs
• Number of logical block addresses available using LBA mode
• Number of physical cylinders, heads, and sectors available in P-CHS mode
• Number of logical cylinders, heads, and sectors in the current translation L-CHS mode
• Transfer modes (and speeds) supported
• Manufacturer and model number
• Internal firmware revision
• Serial number
