What was the primary advancement of the EDVAC over the ENIAC?

ENIAC, one of the earliest electronic computers, had to be manually rewired using switches and cables every time a new program needed to run. This made reprogramming extremely slow and labour-intensive.

EDVAC improved on this by introducing the stored-program concept: both the program's instructions and its data were held together in the computer's own memory, so a new program could be loaded and run electronically instead of by physically rewiring the machine. This idea, closely associated with John von Neumann, became the foundation of virtually all modern computer architecture.

Both machines used vacuum tubes, and EDVAC was not dramatically smaller or reliably faster in every case, so those features do not capture what actually set it apart. The defining leap was architectural: moving from a hand-wired machine to one that could store and execute its own instructions from memory.