In 1937, the ABC (Atanasoff-Berry Computer) was started to develop by John Vincent Atanasoff and graduate student Cliff Berry, which stands for. Although the ABC computer was continuing in the development phase at the Iowa State College in 1937, later continued at Iowa State University until 1942.
More than 300 vacuum tubes were used by the Atanasoff-Berry Computer for digital computation. It had no CPU as it was not able to programming. On 19 October 1973, it was declared by US Federal Judge Earl R. Larson that the ENIAC patent by John Mauchly and J. Presper Eckert was invalid.
In 1943, at the University of Pennsylvania, John Mauchly and J. Presper Eckert started to invent the ENIAC, and it was continuing in the development phase but not completed until 1946. It used about 18,000 vacuum tubes and occupied about 1,800 square feet, weighing almost 50 tons. The first digital computer, the ENIAC is still considered by many people as it was fully functional. But, according to the judge ruled, the first digital computer was ABC computer.