Chapter 9: Hard Disks and Floppy Disks^183
only a single cable for data and control signals, such as SCSIs (Small Computer System
Interface) and IDE/EIDEs (Integrated Drive Electronics/Enhanced IDE). These systems
also allow more than one drive to be connected to the cable. The IDE interface supports two
disk drives on the cable, and the SCSI interface allows u pto seven drives on the same
interface cable. There are special adapters and controllers available to extend the number
of drives that can share an interface. For example, a special EIDE controller is available that
allows eight EIDE devices to share an IDE controller.
Thepower connectoris the standard power connector available from the PC’s power
supply that supplies the disk with 5V and 12V DC power. The logic power and other
circuitry of the disk drive uses 5V, and the spindle motor and head actuator use 12V
power. How much power the drive consumes in watts is something you should know
about your drive to avoid overloading the power supply. This is more important on older
systems than it is on newer ones with 3.5-inch or smaller form factor disk drives. The 3.5-inch
drives use only a fraction of the power that the older 5.25-inch drives require.
If your system has agrounding tab, you may want to use it to create a positive ground
to the PC’s chassis. If the disk drive is mounted directly to the chassis in a drive bay, this
connection is probably not needed. However, if the hard disk is mounted in a plastic or
fiberglass mounting, it’s an excellent idea to connect the grounding tab. Without the
grounding connection, the disk drive may have read, write, or remembering problems.
Thejumperson the disk drive are used to configure the drive as a master or slave on
a shared interface, as well as other configuration settings. See your disk drive documen-
tation for the correct position for the jumpers, as they differ among manufacturers and
even models.
Figure 9-7. The connectors on a standard EIDE/IDE type disk drive. Original photo courtesy of
Western Digital CorporationData connector
Jumpers
Power connector