Base member and hard disk drive (HDD) including the same

A base member including two-step recesses and a hard disk drive (HDD) including the same. The HDD includes a base member; a spindle motor installed in the base member; a data storage disk assembled to the spindle motor; and an actuator rotatably installed in the base member and for moving a read/write head to a desired position on the disk, wherein the base member includes: a first floor surface disposed in a region facing the disk and having a center portion in which the spindle motor is installed; a shroud formed on a circumference of the first floor surface and extending the exterior circumference of the disk; and two-step recesses formed in an operating region of the actuator, wherein the two-step recesses comprise a first step recess formed on the first floor surface and a second step recess formed on a floor surface of the first step recess. An extended shroud is formed in an upstream side of an operating region of the actuator of the base member, protrudes from the shroud, and extends along the exterior circumference of the disk. An air block is installed in a downstream side of the operating region of the actuator.