The AS/400 is an IBM minicomputer for small business and departmental users, released in 1988 and still in production under the name iSeries. The AS/400 is an object oriented system with an integrated database. All necessary software to run this computer is included and integrated. Only with the Linux distributions you will find similar out of the box functionality.
Features include a menu-driven interface, multi-user support, terminals and printers (IBM 5250), security, communications and an extensive library-based operating system, OS/400. The big selling point is said to be that applications run and run without modification.
The machine survives because the Hardware abstraction layer of its microcode allows the operating system and application programs to take advantage of advances in hardware and software without recompilation. This means that a program written and compiled on a S/38 does runs as a native 64 bit program. The HAL allows a system that costs $9000 to run the exact same operating system and software as a $2 million system
Commands in the Command Language (CL) are promptable and most provide cursor sensitive help to make entering parameters easier. A command consist of a three letter verb and a subject part. This makes it easy to understand CL code. Examples: