First Draft of a Report on the EDVAC

Von Neumann wrote the report by hand while commuting by train to Los Alamos, New Mexico and mailed the handwritten notes back to Philadelphia.

Von Neumann describes a detailed design of a "very high speed automatic digital computing system."

He divides it into six major subdivisions: a central arithmetic part, CA; a central control part, CC; memory, M; input, I; output, O; and (slow) external memory, R, such as punched cards, Teletype tape, or magnetic wire or steel tape.

For multiplication and division, he proposes placing the binary point after the sign bit, which means all numbers are treated as being between −1 and +1[a] and therefore computation problems must be scaled accordingly.

Von Neumann's design is built up using what he call "E elements," which are based on the biological neuron as model,[1][2] but are digital devices which he says can be constructed using one or two vacuum tubes.

Circuits are to be synchronous with a master system clock derived from a vacuum tube oscillator, possibly crystal controlled.

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.

A key design concept enunciated, and later named the Von Neumann architecture, is a uniform memory containing both numbers (data) and orders (instructions).

14.0) Von Neumann estimates the amount of memory required based on several classes of mathematical problems, including ordinary and partial differential equations, sorting and probability experiments.

Order types include the basic arithmetic operations, moving minor cycles between CA and M (word load and store in modern terms), an order (s) that selects one of two numbers based on the sign of the previous operation, input and output and transferring CC to a memory location elsewhere (a jump).

The issuance and distribution of the report was the source of bitter acrimony between factions of the EDVAC design team for two reasons.

[3] First, the report was later ruled a public disclosure that occurred more than a year before the EDVAC patent application was filed, thereby rendering the eventual patent unenforceable; second, some on the EDVAC design team contended that the stored-program concept had evolved out of meetings at the University of Pennsylvania's Moore School of Electrical Engineering predating von Neumann's activity as a consultant there, and that much of the work represented in the First Draft was no more than a translation of the discussed concepts into the language of formal logic in which von Neumann was fluent.