Mainframe computers are large systems that usually completely fill one or more rooms. Older makers: Burroughs, Honeywell, IBM, Sperry, Univac. Current makers: Unisys; of IBM compatible mainframes: Fujitsu Ltd., its US subsidiary Amdahl, Hitachi Ltd., IBM. IBM now dominates this market. Most other makers have been merged out of existence. Sperry and Univac merged into Sperry-Univac in 1955. Burroughs and Sperry merged into Unisys in 1986.