The Computers: Software: Operating Systems: (Mainframe Operating Systems )

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. Mainframe Operating Systems Software Computers.

Mainframe computers (colloquially referred to as " big iron " ) are computers used primarily by large organizations for critical applications, bulk data processing, such as census, industry and consumer statistics, enterprise resource planning, and transaction processing . (wikipedia)