IBM SSEC

The IBM Selective Sequence Electronic Calculator, or SSEC, was an electromechanical computer that IBM designed from late 1944 and operated from January 1948 to August 1952. It was a hybrid of roughly 12,500 vacuum tubes in its arithmetic unit and registers and about 21,400 relays for control and slower registers, with most of its data held on paper tape. IBM built it after parting ways with Howard Aiken over credit for the Harvard Mark I, and the astronomer Wallace Eckert of Columbia University supplied its specifications. It stood behind a street-level window on Madison Avenue in New York and gave IBM great publicity. Its design let instructions be treated as data, yet it is usually classed as the last of the programmable calculators because its instructions ran from paper tape, so claims that it was the first stored-program computer remain debated.