Abstract: An apparatus and method for writing servo data to a rotatable disc of a disc drive, the servo data used to control the position of a read/write head adjacent the disc. An internally mounted clock head assembly provides disc angular position information by writing and subsequently reading a clock pattern to and from the disc. A radial position detection assembly identifies the radial position of the head. A control circuit controls the function and position of the head to write the servo data to the disc in response to the disc angular and head radial position information. The clock head assembly and radial position detection assembly remain contained within the disc drive during subsequent field use, and can be configured to detect the application of rotational vibration to the disc drive and to rewrite the servo data.