Workpieces, such as, semiconductor wafers, are continuously manufactured by repetitively alternately switching a common radio frequency power source between a plurality of downstream or in-chamber processing reactors and actively processing one workpiece in a vacuum in an operating one of the processing chambers while simultaneously executing with a robot at atmospheric pressure the overhead tasks relative to next processing another workpiece in the other processing chamber. The active processing of the workpieces in alternate chambers does not overlap, and the robot starts and completes all of its preparatory tasks during the active processing step during the time when a chamber's door is closed thereby providing virtual zero overhead. System architecture allows eliminating all redundant components other than the dual chambers which operate in parallel. For a modest cost increase for the second chamber throughput is trebled and overall costs significantly reduced. Preferred modes include switching a common microwave power source between the pair of processing chambers, pumping down with a common vacuum pump, and stabilizing the chamber pressure with a common throttle valve.