Ada Lovelace Wrote the First Algorithm for a Machine That Was Never Built

Ada Lovelace was 27 years old in 1842 when Charles Babbage asked her to translate a 27-page article by the Italian military engineer Luigi Menabrea on Babbage's still-unbuilt Analytical Engine. She spent nine months on it. The translation itself was straightforward; the more interesting work happened in the margins. Lovelace appended her own footnotes, labeled A through G, that ran to roughly three times the length of the original article and ended up forming the substantive part of the publication when Taylor's Scientific Memoirs printed it in September 1843 under the initials "AAL." The journal didn't print her full name. She was a woman, and married, and these things were complicated.

The centerpiece is Note G. In it Lovelace works out, step by step, how the Analytical Engine's punched cards could be sequenced to compute Bernoulli numbers — a technical sequence in number theory used in formulas for sums of powers of integers. The procedure includes the use of a loop, a stored variable that gets reused, and explicit branching. Historians of computing usually treat it as the first published algorithm specifically intended to be run on a programmable machine. Babbage had written shorter unpublished sequences for himself between 1837 and 1840, but Note G is the first one anyone outside his study saw.

The engine itself, like much of Babbage's life, was never finished. Lovelace died of uterine cancer in 1852 at 36 — the same age her father, Lord Byron, had died. The Pentagon's high-level programming language was named Ada in 1980; the reference manual was approved on her birthday, December 10.