OS/400 is IBM's operating system for its AS/400 and AS/400e line of business computers. Because OS/400 is closely attuned to the AS/400 hardware design and generally comes as part of the basic package, there is no alternative operating system to compete with it. OS/400 is built to operate with the AS/400 logical partition (LPAR) architecture, in which multiple instances of the operating system can run concurrently in different partitions. Among other uses, LPAR is useful when migrating to a new release. The old production system can keep operating in one partition while a new system is being tested.

As the AS/400 has evolved to meet the latest trends in business and information technology, OS/400 and its related software has added support for:

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  • Applications written in the Java programming language
  • The ability to run Windows 2000/NT applications (when certain other products are installed)
  • The Portable Application Solutions Environment (PASE), which supports a subset of the AIX environment so that UNIX applications can be ported and run on the AS/400
  • Lotus Domino, which provides groupware and e-mail from Lotus Notes applications or a standard Web browser
This was last updated in October 2008

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