Harvard Mark III

It was finished at Harvard in 1949 and delivered to the Naval Proving Ground at Dahlgren, Virginia, the following year, which is where the alternative name Aiken Dahlgren Electronic Calculator comes from. The arithmetic was electronic, on the order of five thousand vacuum tubes, while control and peripherals still leaned on relays. The real novelty was storage: eight magnetic drums, in place of the relay registers and paper tape that Mark I and Mark II had made do with.

Instructions lived on their own drums, separate from the data drums. Aiken held to that split long after the von Neumann report had argued the opposite way, and it is precisely that stubbornness that gave the Harvard architecture its name — a term coined after the fact, by people who built things differently. The machine also had a coding scheme that let an operator enter calculations in something closer to formulas than machine code, typed on a typewriter-like unit.