Harvard Mark I

Howard Aiken proposed an automatic calculator in 1937 and persuaded IBM to build it. The Automatic Sequence Controlled Calculator arrived at Harvard in February 1944: 765,000 components, five tons, a fifty-foot drive shaft and a five-horsepower motor keeping the whole thing in step. It worked in decimal across 72 accumulators of 23 digits each. Addition took three-tenths of a second, division a little over fifteen.

Instructions were read from 24-channel punched paper tape while numbers sat in mechanical registers. That strict separation of instruction path from data path is precisely what later became known as the Harvard architecture — a term coined retroactively by people who needed a name for the opposite of von Neumann.

Grace Hopper was among its first programmers and wrote the machine's manual in 1946. At the dedication ceremony Aiken read a press release that barely mentioned IBM, Thomas Watson was furious, and the two institutions stopped speaking; IBM built the SSEC partly out of spite. The Mark I kept computing until 1959, including work for the Manhattan Project.