Seagate ST43401N/ND, ST43402ND user manual

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.