IBM i

OS400 (sometimes referred to as i5/OS) is the core of the iSeries and the thing that makes it the unique system it is.

OS400 includes a very robust variation of the DB2 database.

Generally, OS400 is accessed using a 5250 emulator.

Contrary to popular belief, the OS/400 provides a large number of "Open" resources common on other systems..

• Java
• Apache Web server
• Posix compliant API's accessible from many programming languages.

Originally OS/400, meaning Operating System 400, was for the AS/400, meaning Advanced System 400.

Then IBM came out with variants and re-inventing renaming ... see Names ... such as the AS/36 Advanced System 36, which offered an advanced version of S/36 OS SSP running on the AS/36 one of two flavors:

• M36 Machine 36, which was later discontinued, and
• S36 Environment 36 on the 400.