Embodiments of the invention provide a disk drive that may perform part of a function assignment process without being connected to a special test apparatus. In one embodiment, servo data is written only into dedicated regions of a disk. A function assignment program is stored within the dedicated regions. When a processor is powered on, the processor refers to a state setter and judges whether the function assignment program is to be executed. The state setter is constituted by a nonvolatile memory or a jumper block. The function assignment program includes data relating to servo data writing based on a self-servo writing scheme, and data relating to parameter setup.