In 1961, Scientific Development Corporation introduced the Minivac 601, a simple relay-based electromechanical computer with a primitive memory, all designed by the pioneer of information theory, Claude Shannon. The expensive device attracted few buyers, and was soon upgraded and retargeted for the corporate technical training market. In 1963, E.S.R., Inc. marketed the low-cost Digi-Comp I, which allowed children to construct a simple digital computer, composed entirely of mechanical parts operated by hand. They could then play with it, watching as mechanical versions of “flip-flop” electronic circuits demonstrated Boolean logic computations, solved problems in binary logic, and calculated simple mathematical operations.