that a circuit to compensate for signal delay between the driving signal and a voltage detection signal from the spindle motor driver 54 is installed hereinafter a method of controlling a disc drive using a counter electromotive force according to the present invention will be described in detail first a principle of the counter electromotive force generated in the spindle motor by disturbance is as follows when disturbance such as an external vibration or an external shock makes a fine vibration in a uniform magnetic force the counter electromotive force is thereby generated specifically the spindle motor driving system includes a non rotating portion and a rotating portion a disk is installed on the rotating portion when an external interference is applied to the spindle motor driving system while the spindle motor is rotating a displacement is generated in the rotating portion so that the torque and rotation velocity thereof change such a change instantly changes the current applied to the spindle motor according to the control process of the spindle motor thus referring to equation 1 it can be seen that the counter electromotive force is generated when the current applied to the spindle motor changes a method of obtaining the counter electromotive force includes using a spindle motor voltage and using a position error signal first a method of controlling a disc drive using a counter.