The basic function of a stepping motor controller is to provide the rated current to the motor windings in the shortest possible time. Voltage plays a large part in the performance. Higher voltage forces current into the motor windings faster, helping to maintain high speed torque. Stepping motor controllers can be divided into two types, unipolar and bipolar. Unipolar drives can send current through a motor's windings in only one direction. Unipolar stepping motor controllers tend to achieve better high-speed performance because energizing only half of the coil reduces the winding's inductance. Bipolar units can send current through a motor's windings in both directions, making bipolar a much more flexible than a unipolar stepping motor controller.