BACKGROUND

Data storage devices such as disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.

A disk drive typically comprises a plurality of disks each having a top and bottom surface accessed by a respective head. That is, the VCM typically rotates a number of actuator arms about a pivot in order to simultaneously position a number of heads over respective disk surfaces based on servo data recorded on each disk surface.FIG. 1shows a prior art disk format2as comprising a number of servo tracks4defined by servo sectors60-6Nrecorded around the circumference of each servo track. Each servo sector6icomprises a preamble8for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark10for storing a special pattern used to symbol synchronize to a servo data field12. The servo data field12stores coarse head positioning information, such as a servo track address, used to position the head over a target data track during a seek operation. Each servo sector6ifurther comprises groups of servo bursts14(e.g., N and Q servo bursts), which are recorded with a predetermined phase relative to one another and relative to the servo track centerlines. The phase based servo bursts14provide fine head position information used for centerline tracking while accessing a data track during write/read operations. A position error signal (PES) is generated by reading the servo bursts14, wherein the PES represents a measured position of the head relative to a centerline of a target servo track. A servo controller processes the PES to generate a control signal applied to a head actuator (e.g., a voice coil motor) in order to actuate the head radially over the disk in a direction that reduces the PES.

