Von Neumann's design is built up using what he call "E elements," which are based on the biological neuron as model, but are digital devices which he says can be constructed using one or two vacuum tubes. In modern terms his simplest E element is a two input AND gate with one input inverted (the inhibit input). E elements with more inputs have an associated threshold and produce an output when the number of positive input signals meets or exceed the threshold, so long as the (only) inhibit line is not pulsed. He states that E elements with more inputs can be constructed from the simplest version, but suggests they be built directly as vacuum tube circuits as fewer tubes will be needed.