therefore computation problems must be scaled accordingly. Circuit design Vacuum tubes are to be used rather than relays due to tubes’ ability operate in one microsecond vs. 10 milliseconds for relays. Von Neumann suggests (Sec. 5.6) keeping the computer as simple as possible, avoiding any attempt at improving performance by overlapping operations. Arithmetic operations are to be performed one binary digit at a time. He estimates addition of two binary digits as taking one microsecond and that therefore a 30-bit multiplication should take about 302 microseconds or about one millisecond, much faster than any computing device available at the time. 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. More complex function blocks are to be built from these E elements. He shows how to use these E elements to build circuits for addition, subtraction, multiplication, division and square root, as well as two state memory blocks and control circuits. He does not use Boolean logic terminology. Circuits are to be synchronous with a master system clock derived from a vacuum tube oscillator, possibly crystal controlled. His logic diagrams include an arrowhead symbol to denote a unit time delay, as time delays must be accounted for in a synchronous design. He points out that in one microsecond an electric pulse moves 300 meters so that until much higher clock speeds, e.g. 108 cycles per second (100 MHz), wire length would not be an issue. The need for error detection and correction is mentioned but not elaborated. Memory design A key design concept enunciated, and later named the Von Neumann architecture, is a uniform memory containing both numbers (data) and orders (instructions). "The device requires a considerable memory. While it appeared that various parts of this memory have