In newer designs controlled by a "traction computer," each engine speed step is allotted an appropriate power output, or "kW reference", in software. The computer compares this value with actual main generator power output, or "kW feedback", calculated from traction motor current and main generator voltage feedback values. The computer adjusts the feedback value to match the reference value by controlling the excitation of the main generator, as described above. The governor still has control of engine speed, but the load regulator no longer plays a central role in this type of control system. However, the load regulator is retained as a "back-up" in case of engine overload. Modern locomotives fitted with electronic fuel injection (EFI) may have no mechanical governor; however, a "virtual" load regulator and governor are retained with computer modules.