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3 Fixed disk subsystem description
3.1 Control Electronics
The drive is electronically controlled by a microprocessor, several logic modules, digital/analog modules, and
various drivers and receivers. The control electronics performs the following major functions:
Controls and interprets all interface signals between the host controller and the drive.
Controls read write accessing of the disk media, including defect management and error recovery.
Controls starting, stopping, and monitoring of the spindle.
Conducts a power-up sequence and calibrates the servo.
Analyzes servo signals to provide closed loop control. These include position error signal and estimated
velocity.
Monitors the actuator position and determines the target track for a seek operation.
Controls the voice coil motor driver to align the actuator in a desired position.
Constantly monitors error conditions of the servo and takes corresponding action if an error occurs.
Monitors various timers such as head settle and servo failure.
Performs self-checkout (diagnostics).
3.2 Head disk assembly
The head disk assembly (HDA) is assembled in a clean room environment and contains the disks and actuator
assembly. Helium is constantly circulated and filtered when the drive is operational. No venting of the HDA is
accomplished, as HDA is hermetically sealed.
The spindle is driven directly by an in-hub, brushless, sensor less DC drive motor. Dynamic braking is used to
quickly stop the spindle.
3.3 Actuator
The read/write heads are mounted in the actuator. The actuator is a swing-arm assembly driven by a voice coil
motor. A closed-loop positioning servo controls the movement of the actuator. An embedded servo pattern supplies
feedback to the positioning servo to keep the read/write heads centered over the desired track.
The actuator assembly is balanced to allow vertical or horizontal mounting without adjustment.
When the drive is powered off, the actuator automatically moves the head to the actuator ramp outside of the disk
where it parks.
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Hard Disk Drive Specification