One design decision let computers treat their own instructions as data

Early computers had to be physically rewired to run a different program. The stored-program concept, described in John von Neumann's 1945 report on the EDVAC, instead held both instructions and data in the same memory, letting a machine modify or generate its own instructions on the fly. Nearly every computer built since, from mainframes to phones, still follows this basic architecture.

— John von Neumann, First Draft of a Report on the EDVAC — 1945