The idea that made the modern computer: store the PROGRAM in the same memory as the DATA. Then a tiny loop runs everything — FETCH the instruction the program-counter points at, DECODE it, EXECUTE it, advance the counter, repeat. Because code is just numbers in memory, a program can even rewrite itself. Von Neumann, 1945. Slide to step the machine through a program.
The von Neumann architecture stores instructions and data in one addressable memory, executed by a control unit + ALU via the cycle: FETCH the instruction at the program counter (PC), DECODE it, EXECUTE (often on an accumulator), then advance PC (or jump). Here a stored program LOAD 5 / ADD 3 / SUB 2 / HALT drives the accumulator to 6. Because code and data share memory, programs can be treated as data (compilers, self-modifying code) — and share the ‘von Neumann bottleneck’ of one bus. A fail-loud self-check throws unless the program executes to accumulator = 6. ◆ real computer architecture, node-verified.
A minimal accumulator machine (real CPUs add registers, pipelines, caches, interrupts); the fetch-decode-execute cycle and stored-program principle are exact and universal.