The present invention is directed to a method and apparatus for dynamic
placement of an integration window in a disk drive having a disk surface
with spiral servo information written thereon. A read head is provided
for reading the spiral servo information and generating a read signal
envelope. A repetitive spiral position error, associated with one spiral
of the spiral servo information, is measured. Placement of an integration
window is dynamically adjusted based upon the measured repetitive spiral
position error, so that a read signal envelope read by the read head
appears more towards the center of the integration window than if the
placement of the integration window was not dynamically adjusted. By
adjusting the placement of the integration window, dynamic range is
increased without increasing the size of the integration window.