1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive employing coarse position feedback from a mechanical position sensor to improve format efficiency.
2. Description of the Prior Art
FIG. 1A shows an exploded view of a prior art disk drive comprising a disk 2 rotated by a spindle motor 4, and a head 6 coupled to a distal end of an actuator arm 8 which is rotated about a pivot 10 by a voice coil motor (VCM) in order to actuate the head 6 over the disk 2. The disk 2, spindle motor 4, head 6, actuator arm 8, and VCM are enclosed in a head disk assembly (HDA) comprising a base 9 and a cover 11. The VCM comprises a voice coil 12 coupled to the base of the actuator arm 8 and one or more permanent magnets attached to a yoke 14. When the voice coil 12 is energized with current, the resulting magnetic flux interacts with the magnetic flux of the permanent magnets to generate a torque that rotates the actuator arm 8 about the pivot 10. A tang 16 attached to the actuator arm 8 interacts with a crash stop 18 to limit the stroke of the actuator arm 8, and also provides a latching mechanism (e.g., using a magnet) to maintain the actuator arm 8 in a latched position while the disk drive is powered down. Alternatively, the actuator arm 8 may be parked on a ramp located at the outer periphery of the disk 2 when the disk drive is powered down.
Servo sectors 210-21N are written to the disk 2 to define a plurality of radially-spaced, concentric servo tracks 23 as shown in the prior art disk format of FIG. 1B. The servo tracks 23 define a number of data tracks, wherein each data track is partitioned into a plurality of data sectors and the servo sectors 210-21N are considered “embedded” in the data sectors. Each servo sector (e.g., servo sector 214) comprises a preamble 25 for synchronizing gain control and timing recovery, a sync mark 27 for synchronizing to a data field 29 comprising coarse head positioning information such as a servo track number, and servo bursts 31 which provide fine head positioning information. The coarse head position information is processed to position a head over a target data track during a seek operation, and the servo bursts 31 are processed to maintain the head over a centerline of the target data track while writing or reading data during a tracking operation.
The servo sectors 210-21N reduce the format efficiency by consuming disk space that could otherwise be used for the data sectors. In addition, as the number of servo tracks is increased in order to increase the tracks per inch (TPI), the servo track address size increases due to the increased number of bits required to identify each servo track. Consequently, the servo sectors 210-21N consume even more disk space per data track as the TPI increases.
There is, therefore, a need to improve the format efficiency of a disk drive by reducing the size of the servo sectors and therefore the amount of disk space consumed by the servo sectors.