The ENIAC built by Eckert and Mauchly in 1946 was thought to have been the world's first electronic digital computer. But in fact the less well known Atanasoff-Berry Computer or ABC built in 1937-1942 was the first.
Built by John Vincent Atanasoff and Clifford Berry at Iowa State University the ABC incorporated several major innovations in computing. It introduced the ideas of binary arithmetic, regenerative memory and logic circuits.
Although it had never been patented the ABC was officially recognised as the first following a court trial in 1972 where the presiding judge ruled that ENIAC had been influenced by the work of John Vincent Atanasoff.