Hardware Reference
In-Depth Information
Of these interfaces, only ST-506/412 and ESDI are what you could call true disk-
controller-to-drive interfaces, and they are obsolete. Non-ATA versions of IDE were used
primarily in the IBM PS/2 systems and are also obsolete. Current SCSI, ATA, and SATA
are system-level interfaces that usually internally incorporate a chipset-based controller
interface. For example, many SCSI, PATA, and SATA drives incorporate the same basic
controllercircuitryinsidetheactualdrive.TheSCSIinterfacethenaddsanotherlayerthat
connects between the drive controller and the PCI (or ISA) bus, whereas PATA and SATA
haveamoredirectconnectionfromthecontrollertotheATbusattachmentinterface.Des-
pitetheirdifferences,wecallaSCSI,PATA,orSATAcarda host interface adapter instead
of a controller card because the actual controllers are inside the drives. Virtually all mod-
ern disk drives use SATA or PATA interfaces to connect to a system.
IDE Origins
Any drive with an integrated controller could be called an IDE drive, although normally
whenwesay IDE ,wereallymeanthespecificversionofIDEcalledATA.Nomatterwhat
you call it, combining the drive and controller greatly simplifies installation because no
separate power or signal cables run from the controller to the drive. Also, when the con-
troller and drive are assembled as a unit, the number of total components is reduced, sig-
nal paths are shorter, and the electrical connections are more noise-resistant. This results
in a more reliable and less expensive design than is possible when a separate controller,
connected to the drive by cables, is used.
Placing the controller, including the digital-to-analog encoder/decoder (endec), on the
driveoffersaninherentreliabilityadvantageoverinterfaceswithseparatecontrollerssuch
as ST506 and ESDI. Reliability is increased because the data encoding, from digital to
analog, is performed directly on the drive in a tight noise-free environment. The timing-
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