A magnetic disk apparatus includes magnetic disks stacked on a rotating shaft,
arms supporting magnetic heads, a rotary actuator for moving the arms, and a housing
forming at least a part of an arcuate-shaped shroud which substantially surrounds
a portion of side surfaces of the magnetic disks so as to define a gap between
the shroud and the portion of the side surfaces of the magnetic disks. The arcuate-shaped
shroud has portions delimiting an open space adjacent to another portion of the
side surfaces of the magnetic disks which is located on a downstream side of the
arms relative to an air flow which moves on surfaces of the magnetic disks. A bypass
channel provides air flow to the disks in a region of the open space at a reduced
pressure on the downstream side of the arms with respect to pressure at an upstream
side of the arms.
