Hardware Reference
In-Depth Information
wasnecessarybecauseitwasknownthatadiskcontrollerneverwouldneedmorethan40
of the ISA bus lines. Smaller 2 1/2-inch ATA drives found in notebook computers use a
superset 44-pin or 50-pin connection, which includes additional pins for power and con-
figuration. The pins from the original ISA bus used in ATA are the only signal pins re-
quired by a standard-type AT hard disk controller. For example, because a primary AT-
style disk controller uses only interrupt request (IRQ) line 14, the primary motherboard
ATAconnectorsuppliesonlythatIRQline;nootherIRQlinesarenecessary.Evenifyour
ATAinterfaceisintegratedwithinthemotherboardchipsetSouthBridgeorI/OController
Hub chip (as it would be in newer systems) and runs at higher bus speeds, the pinout and
functions of the pins are still the same as the original design taken right off the ISA bus.
See Motherboard Connectors ,” p. 214 ( Chapter 4 , Motherboards and Buses ”).
See The ISA Bus , p. 230 ( Chapter 4 ) .
Note
Many people who use systems with ATA connectors on the motherboard believe that a hard
disk controller is built into their motherboards, but in a technical sense the controller is ac-
tually in the drive. Although the integrated ATA ports on a motherboard often are referred to
as controllers, they are more accurately called host adapters (although you'll rarely hear this
term). You can think of a host adapter as a device that connects a controller to a bus.
Eventually,the40-pinATAconnectoranddriveinterface designwasplacedbeforeoneof
the ANSI standards committees that, in conjunction with drive manufacturers, ironed out
some deficiencies, tied up some loose ends, and then published what was known as the
CAM ATA (Common Access Method AT Attachment) interface. The CAM ATA Com-
mittee was formed in October 1988, and the first working document of the ATA interface
was introduced in March 1989. Before the CAM ATA standard, many companies, such
as Conner Peripherals (which later merged with Seagate Technology), made proprietary
changes to the original interface as designed by CDC. As a result, many older ATA drives
from the late 1980s are difficult to integrate into a dual-drive setup because minor differ-
ences in the interfaces can cause compatibility problems among the drives. By the early
1990s,mostdrivemanufacturersbroughttheirdrivesintofullcompliancewiththeofficial
standard, which eliminated many of these compatibility problems.
Some areas of the ATA standard have been left open for vendor-specific commands and
functions.Thesevendor-specific commandsandfunctionsarethereasonitisimportant to
usetheOEM-specificprogramsfortestingATAdrives.Toworktofullcapability,thedia-
gnosticprogramyouareusingtypicallymustknowthespecificvendor-uniquecommands
forremappingdefects.Unfortunately,theseandotherspecificdrivecommandsdifferfrom
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