(Atanasoff-Berry Computer) The first electronic digital computer. Completed in 1942 by Iowa State Professor John Atanasoff and graduate student Clifford Berry, it employed many of the principles of all future computers. For example, although physically in the form of rotating drums, its memory used capacitors that were constantly being recharged like today's dynamic RAM.

It used a standard IBM card reader for input and an odometer-like device for output. For interim storage, Atanasoff devised a base-2 punch and reader that could very quickly store 1,500 bits on paper sheets by electrostatically burning holes in them. The ABC could solve 29 linear equations with 29 unknowns in one 24-hour day, a marvel for its time.

It Took Years for Recognition
John Mauchly, cobuilder of the ENIAC, began corresponding with Atanasoff in 1940 and visited him in 1941. Although Eckert and Mauchly's machine gained international attention, the ABC was recognized years later. A 1973 court overturned an ENIAC patent, stating that the basic ideas of the modern computer came from Atanasoff. In 1990, 87-year-old Atanasoff was awarded the National Medal of Technology. Four years later, an Iowa State University team started to build a replica of the ABC. It took three years to complete, but worked exactly as it was supposed to.