1943, Los Alamos, New Mexico.
A group of scientists was developing the most terrifying weapon in human history—the atomic bomb. They needed to calculate the critical mass of nuclear fission, involving massive mathematical operations.
A man in a suit walked into the laboratory. He wasn’t a physicist or an engineer—he was a mathematician—but he could calculate faster in his head than a computer.
He looked at the scientists’ calculation tasks and said, “You need a better computer.”
This man was named John von Neumann. He was about to design the blueprint for modern computers.
Genius Among Geniuses#
von Neumann was born in 1903 in Budapest, Hungary, to a Jewish family.
He was a legendary genius from childhood. At 6, he could mentally divide two 8-digit numbers. At 8, he mastered calculus. At 12, he read Borel’s function theory.
Once, someone asked him, “How did you calculate that problem you just did mentally?”
von Neumann said confusedly, “I just calculated it directly.”
He couldn’t explain his thought process—for him, those complex calculations were as natural as breathing.
Later he immigrated to America and became a professor at the Institute for Advanced Study in Princeton. He made pioneering contributions in mathematics, physics, economics, meteorology, and many other fields. Nobel Economics Prize winner Paul Samuelson said: “von Neumann was the smartest genius of this century.”
The ENIAC Revelation#
In 1943, the U.S. Army funded the construction of the world’s first electronic computer—ENIAC (Electronic Numerical Integrator and Computer).
ENIAC was a behemoth: weighing 30 tons, occupying 170 square meters, with 18,000 vacuum tubes. It could perform 5,000 additions per second, 1,000 times faster than previous mechanical calculators.
But ENIAC had a fatal flaw: Programming was too troublesome.
ENIAC’s programs were “hard-wired”—to change the program, you had to rewire. Engineers had to unplug hundreds of cables and plug them into new positions. Changing a program could take days.
After von Neumann visited ENIAC, he immediately saw the problem. He thought: Why not store the program in memory too? Then changing the program would be as simple as changing data.
The EDVAC Report#
In 1945, von Neumann wrote a report: “First Draft of a Report on the EDVAC.”
In this report, he described a new computer architecture, later called the von Neumann Architecture.
The core idea was: Stored Program.
Before this, computer programs were hard-wired, with data and instructions stored separately. von Neumann proposed: Programs and data should be stored in the same memory, and the computer should read instructions from memory and execute them.
This way, changing the program only required modifying the instructions in memory, not rewiring.
The von Neumann Architecture#
The von Neumann Architecture contains five parts:
1. Arithmetic Logic Unit (ALU) Responsible for executing arithmetic operations (addition, subtraction, multiplication, division) and logic operations (AND, OR, NOT).
2. Control Unit Responsible for reading instructions from memory, decoding instructions, and controlling the ALU to execute.
3. Memory Stores programs and data. Programs and data are stored in the same space.
4. Input Devices Get data from outside, such as keyboards, card readers.
5. Output Devices Output results, such as displays, printers.
These five parts are connected by a Bus, with data and instructions flowing between them.
The workflow is:
- The control unit reads the next instruction from memory
- The control unit decodes the instruction, determining what to do
- If it’s a calculation instruction, the control unit tells the ALU to execute
- If it’s an input/output instruction, the control unit controls the input/output devices
- Return to step 1, continue executing the next instruction
This simple loop is the basic principle of how computers work. Until today, your phone, your computer, essentially repeats this loop—just billions of times faster.
Controversy: Was This von Neumann’s Work Alone?#
The von Neumann Architecture is called the “von Neumann Architecture,” but was it really his invention alone?
Historians have different views.
ENIAC designers J. Presper Eckert and John Mauchly believed they first proposed the stored program concept. von Neumann just wrote their ideas into the report.
Another computing pioneer Herman Goldstine believed von Neumann’s contribution was systematization and theorization—he integrated scattered ideas into a complete architecture and clearly described it in mathematical language.
Regardless, von Neumann’s report had enormous impact. It became the “bible” of computer design, and almost all subsequent computers adopted this architecture.
The von Neumann Bottleneck#
The von Neumann Architecture has an inherent problem, later called the von Neumann Bottleneck.
The problem is: the CPU (ALU + Control Unit) and memory are separate. The CPU executes instructions very fast, but reading data from memory is relatively slow. The CPU often has to wait for memory, wasting performance.
To use an analogy: the CPU is like a super-fast chef, memory is like a slow warehouse. The chef can chop and cook in seconds, but going to the warehouse to get ingredients takes minutes. The chef spends most of the time waiting for ingredients.
Modern computers use various techniques to alleviate this problem: Cache, Pipeline, Branch Prediction. But the von Neumann Bottleneck always exists and remains one of the core challenges in computer architecture design.
von Neumann’s Legacy#
von Neumann died of cancer in 1957 at age 53.
He published over 150 papers in his lifetime, covering mathematics, physics, economics, computer science, and many other fields. He was called “the last polymath”—after him, science became increasingly specialized, and few could make pioneering contributions in multiple fields.
In the computer field, the von Neumann Architecture remains dominant. Although other architectures have been proposed (such as Harvard architecture, dataflow architecture), the simplicity and generality of the von Neumann Architecture made it the standard for computer design.
Every time you turn on a computer, start a phone, run a program, you’re using von Neumann’s ideas.
From Theory to Practice#
Turing defined the theoretical boundaries of computation; von Neumann designed the architectural blueprint for computers.
Now, it was time to turn the blueprint into real machines.
In 1946, ENIAC officially operated at the University of Pennsylvania. It was the world’s first general-purpose electronic computer, marking the beginning of the computer age.
The story of ENIAC continues tomorrow.
Today’s Key Concepts#
von Neumann Architecture A way of organizing computers, with the core feature being “stored program”—programs and data stored in the same memory. Contains five parts: ALU, control unit, memory, input devices, output devices. Remains the foundation architecture for most computers today.
von Neumann Bottleneck An inherent defect of the von Neumann Architecture: data transfer speed between CPU and memory limits overall performance. CPU speed is far faster than memory access speed, causing the CPU to often wait for data. Modern computers use cache and other techniques to alleviate this problem.
Bus A channel for transmitting data between computer components. Data bus transmits data, address bus transmits address information, control bus transmits control signals. Bus bandwidth determines data transfer speed.
Discussion Questions#
- The von Neumann Architecture stores programs and data in the same memory. What are the advantages? What are the disadvantages?
- If you could travel back to 1945 and meet von Neumann, what question would you ask him?
Tomorrow’s Preview: The Birth of ENIAC—the world’s first electronic computer, a 30-ton behemoth that changed the world.