Abstract: Head disc assembly serial number information is encoded in the servo bursts recorded during servo track writing. Specifically, the HDA serial number information is written to the disc during disk manufacture as part of the Servo Track Writing process in between the normal servo frames. The serial number is preferably written on preexisting unique system (non-user) tracks in-between normal servo frames. The encoded serial number can be retrieved by increasing the sampling interval of the servo information, i.e., by over-sampling the servo information. More specifically, by writing the serial number in a servo burst exactly in the middle of two normal servo frames, the information can be retrieved by 2× over-sampling routines called by system diagnostic routines or disc drive certification routines. In addition, a disc drive apparatus having a retrievable encoded head disc assembly serial number is provided.