A head stack assembly includes a head stack assembly main body moving a
head across a disk, and rotating around a predetermined pivot shaft. The
head stack assembly also includes a center of gravity compensation
portion coupled to the head stack assembly main body and compensating for
imbalances in the center of gravity of the head stack assembly main body
to be not more than a reference imbalance value. The reference imbalance
value is based on an imbalance value of the center of gravity of the head
stack assembly main body measured with respect to a rotational center of
the pivot shaft.