Hardware Reference
In-Depth Information
Over the years, head designs have evolved from the first simple ferrite core designs into the
magneto-resistive and giant magneto-resistive types available today.
Head Actuator Mechanisms
Possibly more important than the heads themselves is the mechanical system that moves
them: the head actuator. This mechanism moves the heads across the disk and positions
themaccuratelyabovethedesiredcylinder.Manyvariationsonheadactuatormechanisms
are in use, but all fall into one of two basic categories:
The use of one or the other type of actuator has profound effects on a drive's performance
and reliability. The effects are not limited to speed; they also include accuracy, sensitivity
to temperature, position, vibration, and overall reliability. The head actuator is the single
most important specification in the drive, and the type of head actuator mechanism in a
drive tells you a great deal about the drive's performance and reliability characteristics.
Table9.10
showsthetwotypesofHDDheadactuatorsandtheaffectedperformancechar-
acteristics.
Table 9.10 Characteristics of Stepper Motor Versus Voice Coil Drives
Stepper Motor Actuators
A stepper motor is an electrical motor that can “step,” or move, from position to position,
with mechanical detents or click-stop positions. If you were to grip the spindle of one of
these motors and spin it manually, you would hear a clicking or buzzing sound as the mo-
tor passed each detent position with a soft click.
Steppermotorscan'tpositionthemselvesbetweensteppositions;theycanstoponlyatthe
predetermined detent positions. The motors are small (between 1 inch and 3 inches) and
