Chapter 9: Hard Disks and Floppy Disks^185
such as adding the endec into the drive. ESDI drives were used on high-end systems from
brand-name manufacturers in the late 1980s, but soon the lower-cost, higher performing
IDE drives made it largely obsolete, except on some high-end proprietary systems.IDE
TheIDE(IntegratedDriveElectronics)interface,oneofthemorepopularinterfacetechnologies
inusetoday,wasoriginallydevelopedasanalternativetotheexpensiveSCSItechnology.As
its name implies, IDE technology integrates the disk controller as a part of the disk drive.
IDE is also known as AT Attachment (ATA) interface. Since the drive controller is a part of
the disk drive, IDE devices can usually be connected directly to the motherboard or by using
a pass-through board. IDE interface cards are usually multifunction cards that not only
support the hard disk, but a floppy drive, a game port, perhaps a serial port, and more.
An ATA IDE drive should never be low-level formatted. A low-level format, which
scans the disk media for defects and sets aside any sectors with defects, is performed at
the factory during manufacturing and should never be performed by a user or a technician.
Only a high-level format (such as that performed by the Windows formatting function) is
necessary to prepare the disk partitions for the operating system and data.
The standard IDE interface supports up to two 528MB drives. EIDE (Enhanced IDE), also
called ATA-2, is a newer version of IDE that increases the capacity of the interface to four
multigigabytedrives.RecentdevelopmentshaveextendedtheEIDEinterfacetoeightdrives.
Another standard closely related to the EIDE interface standard is theATAPI (ATA
Packet Interface), an interface standard for CD-ROMs and tape drives that connect to
common ATA (IDE) connectors.SCSI Interface
TheSmall Computer Systems Interface (SCSI),pronounced “scuzzy,” is not an interface
standard in the way that IDE is. It is a system standard that is made u pof a collection of
interface standards covering a range of peripheral devices, including hard disks, tape
drives,opticaldrives,CD-ROMs,anddiskarrays.UptoeightSCSIdevicescanconnectto
asingleSCSIcontrollerbysharingthecommoninterface,calledaSCSIbusorSCSIchain.
Like IDE devices, SCSI controllers are built into the devices. As SCSI devices are
added to the SCSI bus, each device is assigned a unique device number to differentiate it
from the other devices. The SCSI controller communicates with the devices on the bus by
sending a message encoded with the unit’s device number, which is also included in any
replay sent by the device. A SCSI bus must be terminated to prevent unclaimed or misdi-
rected messages from bouncing back onto the bus.FC-AL Interface
TheFC-AL (Fiber Channel-Arbitrated Loop), or fiber channel for short, is used with very
large systems or networks that incorporate high bandwidth and high-end disk arrays. It
is a very high-availability type of system, which means that it has built-in data recovery
and fault-tolerant components. As you might guess, fiber channel disks are much more
expensive than disks using other interfaces, including SCSI devices.