Higher TPI HDD requires lower disturbance and higher error rejection capability. One of the limitations to achieve high error rejection capability is the dynamics of the actuator. Dual stage actuator (DSA) has been considered to replace single stage actuator (SSA) someday because of system dynamics difference and more freedom in servo design that may avoid the constraint of single stage actuator dynamics on servo. SSA and DSA were compared based on their dynamics, servo designs, and TMR benefits. The extendibility and limitations of both systems were studied. The criteria on when DSA would be implemented are also discussed.

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