Model 204 is a database management system for IBM and compatible mainframe computers, “born” 1965 October 13,:66 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.:4
Model 204 relies on its own type of bitmap index, originally devised by Professor Patrick E. O'Neil, and also combines the use of hash table, B-tree, and record list technologies to optimize speed and efficiency of database access.
Although M204 is a pre-SQL (and pre-relational) database product, it is possible to manually map the files of an M204 database to approximate SQL equivalents and provide some limited SQL functionality using Model 204 SQL Server.
Model 204 is most commonly used in government and military applications. Among other things, it runs Australia's social security system (Centrelink). It is used commercially in the UK by Marks & Spencer. It is also used at the Ventura County Property Tax system in California, the Harris County, Texas, Justice Information Management System, and in the New York City Department of Education's Automate The Schools system. An informal list of past and present Model 204 users, compiled in 2010, identified more than 140 organizations worldwide.
Add-on products are available from Sirius Software, Inc.
Database Programmer's Toolkit is a freeware PC-based emulation.
See also 
- Scinta, Gina (2005-10-10). "Model 204 v6r1: Opening New Doors". Computer Corporation of America. Retrieved 2012-10-26.
- "Model 204, A Novel DBMS and Application Platform". Sirius Software. Retrieved 2012 October 26.
- O'Neil, Patrick (1987). "Model 204 Architecture and Performance". Proceedings of the 2nd International Workshop on High Performance Transaction Systems. Springer-Verlag. pp. 40–59.
- Sandy Stanhope, Database Administrator. "What is Model 204?". The Youngstown State University Computing Newsletter. Department of Computer Services. Retrieved 11 January 2008.
- "Rocket Model 204 SQL Server Users Guide". Rocket Software. 2012 May. Retrieved 2012-10-27.
- "County of Ventura Technology Infrastructure Strategic Plan". Gartner. 2005-07-13. p. 43. Retrieved 2012-10-25.
- "Model 204 Civil Inquiry Manual". Harris County, Texas. 2007 June. Retrieved 2012-10-25.
- Paul Keshvari et al. (2010). "M204 Client List". Retrieved 2012 October 28.
- http://www.ebizq.net/news/12526.html; acquired June 13, 2010
- Model 204 at Rocket Software
- Model 204 at Sirius Software
- An example of Model 204 User Language programming
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