The Free On-line Dictionary of Computing (30 December 2018):

first generation computer

    A prototype computer based on vacuum tubes
   and other esoteric technologies.  Chronologically, any
   computer designed before the mid-1950s.  Examples include
   Howard Aiken's Mark 1 (1944), Maunchly and Eckert's
   ENIAC (1946), and the IAS computer.

   (1996-11-22)