Model 204 is a database management system for IBM and compatible mainframe computers, “born” 1965 October 13, and first deployed in 1972. It incorporates a programming language and an environment for application development. Implemented in assembly language for IBM System/360 and its successors, M204 can deal with very large databases and transaction loads of 1000 TPS.Model 204 relies on its own type of bitmap index, originally devised by Professor Patrick E.