1. A parallel digital processing system comprising: a databus; a plurality of asynchronous, digital processing units connected to said databus, each processing unit receiving data signals over said databus and producing output command signals, the processing units operating in parallel and redundant one to the next; and a databus voter connected to said databus for receiving the output command signals from each of the processing units and, responsive to a predetermined voting algorithm, outputting onto said databus as the voted command signal a selected one of said received command signals.