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ST43401N/ND, ST43402ND User’s Manual, Rev. B 5
The drive contains all the circuits and mechanical devices necessary to record
data on and recover it from its discs. The drive requires DC voltage inputs from
an external power supply, which you must supply. The DC power cable is
available as an accessory.
The ST43401N/ND drives consist of a head and disc assembly (HDA) with two
circuit boards, and the ST43402ND drive consists of an HDA and three circuit
boards. Each drive’s HDA and circuit boards are mounted on a common
chassis. The circuit boards contain the electronics required for drive opera-
tion. The HDA is a sealed unit containing the electromechanical components
used for data retrieval and storage . These components include the discs,
spindle, drive motor, actuator, heads, and preamplifiers.
The eleven discs provide the recording medium for the drive. These discs are
mounted on a spindle, and the spindle is coupled directly to the drive motor.
The drive motor rotates the discs at 5,400 RPM and produces a circulation of
air within the sealed HDA.
The built-in SCSI controller directs all drive functions, receives commands
from the initiator (host computer), interprets them, and then transfers the
necessary commands to the drive. The controller therefore allows the initiator
to start an operation and then disconnect to service another device. Refer to
the reference manual for a description of interface functions.
All drive operations are related to data recovery and storage (normally
referred to as reading and writing). The actual reading and writing is performed
by heads that are positioned over the rotating discs’ recording surfaces. There
is one head for each data surface. The heads are positioned in such a way that
data is written in concentric tracks around the disc surfaces (see Figure 3).
Before any read or write operation can be performed, the controller must
instruct the drive to position the heads over the desired cylinder (called
seeking) and use the head located over the surface (head selection) where the
operation is to be performed.
The heads are mounted on the actuator, and the actuator moves the heads
over the rotating discs. There are 22 heads—a servo head to sense actuator
positioning, and 21 data heads used for data transfers to and from the discs.
The actuator has a voice coil that moves in a permanent magnetic field in
response to signals from the servo positioning circuitry. The voice coil moves
the heads in an arc across the rotating discs.