EDVAC report

The First Draft of a Report on the EDVAC — universally called the EDVAC report — is a 101-page typescript written by John von Neumann and distributed on 30 June 1945. In fewer than a hundred pages it described the architecture of a computer that would keep its instructions in the same memory as its data — the design almost every computer built since has followed. It is arguably the most influential document in the history of computing, and also one of the most contested.

What the report actually says

The report describes EDVAC — the Electronic Discrete Variable Automatic Computer, the Moore School's planned successor to ENIAC. Its machine had:

• A memory of roughly 5.5 kilobits (mercury delay lines, 32 bits per word) holding numbers and instructions together — the stored program
• A central arithmetical organ — the CA, today's ALU/CPU — that fetched instructions from memory and executed them in sequence
• Control logic to interpret instructions, plus input, output, and secondary storage
• A stored-program fetch-execute cycle: read instruction → decode → read operand → operate → next — the loop every processor still runs
• Conditional branching: an instruction could redirect control based on a computed result — the mechanism that makes loops and decisions possible

The draft also laid out an instruction-set vision — numbered operations, not just wiring — and treated the machine abstractly enough that it reads like a design for all computers, not one. It even included a neurological metaphor (organs, neurons) that helped and hindered the field in equal measure.

Why "stored program" is the idea

Before the EDVAC report, a machine's sequence of operations was its wiring or its card deck — ENIAC's operators reprogrammed by hand-cabling panels for days. The EDVAC idea makes the program a string of numbers in memory: write it, store it, change it in software, run it. The machine can even modify its own program — which is what makes compilers, interpreters, and every layered software abstraction possible. The concept is so fundamental it no longer has a name in everyday talk; it is just "how computers work."

The controversy

The report circulated under von Neumann's name alone — he was the one who wrote it up — but the ideas had been worked out jointly with J. Presper Eckert, John Mauchly, and the Moore School team. Eckert and Mauchly were furious; the uncredited publication cost them both the patent they wanted and, they felt, the credit. The Army judged the stored-program concept unpatentable because the report had already made it public. The resulting legal and personal rift shaped who got remembered: "von Neumann architecture" stuck as the name, though historians generally credit the design as a group product.

Legacy

• The term "von Neumann architecture" descends from this document — though purists note its bottleneck (one bus, memory and code contending) is now called the von Neumann bottleneck.
• Its descendants ran within three years: the Manchester Baby first executed a stored program in 1948, and EDSAC ran the first full working stored-program computer in 1949. EDVAC itself — the machine the report described — was not finished until 1951, overtaken by the very designs it inspired.
• Every programming language, from FORTRAN to AdaLogic BASIC, exists because instructions could finally live in memory and be treated as data.

See also

• John von Neumann
• Manchester Baby
• EDSAC
• The first programmers
• History of Programming

References

1. von Neumann, John. "First Draft of a Report on the EDVAC" (Moore School, 1945).
2. Aspray, William. John von Neumann and the Origins of Modern Computing (MIT Press, 1990).
3. Goldstine, Herman H. The Computer from Pascal to von Neumann (Princeton UP, 1972).