The basic function of a step motor driver 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. Step motor drivers can be divided into two types, unipolar and bipolar. Unipolar controls can send current through a motor's windings in only one direction. Unipolar step motor drivers 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 step motor driver.