RECORDING SERVO INFORMATION BELOW A DATA SURFACE IN A HOMOGENEOUS MEDIUM.

Design characteristics are given for a disk in which servo information is recorded in a lower layer of a magnetic medium, sufficiently thick that a nonsignal region exists between this layer and data written in a surface layer. The servo tracks are first written by a servo writer whose write head has sufficient ampere-turn capability, to record through the total thickness of the medium. After the servo signal has been recorded, a DC or AC biased erase signal of lower intensity is applied, creating a nonsignal region between the surface and a remnant lower layer of servo information. Data is written in the surface layer using baseband partial penetration or AC bias recording at significantly reduced field. Prior to the next write, the track is DC or AC erased with a magnetic field whose strength is less than the initial erase field, but larger than the data write field.