While all three technologies provide very good ESD protection capabilities, the benefits of the Uni-directional and Bi-directional protection devices differ from the Rail-to-Rail Devices. Uni-directional and Bi-Directional devices require only one reference voltage. They have good surge protection capability and have a lower cost per protected line. They are ideal for medium to high speed applications. The Rail-to-Rail devices require two reference voltages and are geared to Ultra high speed applications.