compared to a fixed range of voltage threshold to determine if the spindle motor is over speed or under speed in the pre defined process 116 abnormalities would arise if there is an over speed or under speed the output from 116 will be fed to another predefined process 118 where the duration of the voltage output from 114 will be monitored if the duration of the voltage output from 114 is less than a certain pre defined time the abnormality will not be considered and the trigger 120 will not be activated the trigger 120 is triggered when the spindle over speed or under speed for a significant duration once the trigger 120 is activated the actuator will be retracted 122 to the landing zone and the servo will be reset to a known state 124 fig3 further illustrates the pre defined process 116 the voltage from 114 is split to two 126 the split voltage is then fed to two comparators 128 and compared to a higher and a lower threshold voltage 130 at each comparator the resultant digital output state is determined and the outputs are fed through an or gate to provide a single resultant output at 132 the digital output at 132 may be a high state or a low state depending on the speed of the spindle motor fig4 further illustrates the pre defined process 118 the resultant output from 132 is split into two at 134 and fed to a delay filter 136 the resultant from the delay filter at 136 is then fed to an and gate at 138 to determine the resultant digital output the delay filter monitors the duration of the spindle speed by comparing to a predefined.