First-Generation Vacuum-Tube Computers

First-generation vacuum-tube computers were the earliest class of electronic digital computers, built with vacuum tubes for their logic circuitry before the shift to transistors in the late 1950s. The Ferranti Mark 1, completed in 1951, is credited as the first commercially available stored-program computer, while the LEO I, built the same year for the J. Lyons catering company, became the first computer used for routine business applications. Germany's Zuse Z22 followed in 1955 as a commercial vacuum-tube machine sold in the dozens across Europe. In the United States, the IBM 650 became the first computer to sell in the thousands, bringing electronic computing to a wide range of businesses and universities during the 1950s. These four machines mark the transition of computing from one off scientific instruments to genuine commercial products built with vacuum-tube technology.