The earliest computers were fixed programmed, for e.g. calculator etc. Changing the program of a fixed-program machine to perform a different function, for e.g. word processing etc required re-wiring, re-structuring, or re-designing the machine which was a hugely cumbersome task that meant altering the electronic circuitry by setting switches and inserting patch leads to route data and to control signals between various functional units and so on.

John von Neumann who was a Hungarian American mathematician, an early computer scientist and the inventor of the merge sort algorithm described a computer architecture in which the data and the program (instructions) are both stored in the computer's memory in the same address space in his First Draft of a Report on the EDVAC (distributed on June 30, 1945); a computer that by design includes an instruction set and can store in memory a set of instructions (a program) that details the computation. The idea of the stored-program computer changed everything.

This single-memory, stored program architecture is to this day the basis of modern computer design and is commonly called von Neumann architecture as a result of von Neumann's paper.