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