The IBM AS400 is a minicomputer released in 1988 aimed at departmental and/or general computing.

It was the successor platform to IBMs System38 which had reached its computational ceiling. However numerous core feature technologies from its predecessor remained such as the object based architecture which facilitates greater scaling capabilities across its processors.

Unlike multiprocessor/core consumer grade PCs whose applications need to be explicitly written and compiled to take advantage of more than a single processor, the same program will scale from a base configured AS/400 to the top of the line model and offer predictable, linear performance gains due to the architecture of the system. And these machines have offered this functionality since the late 80s!

Originally the systems were configured with 55 or 75Mhz CISC CPUs which shared a similar instruction set with the System38 machines they were replacing. In 2002 IBM transitioned the entire AS400 line over to RISC based POWER4 series of processors and all subsequent offerings are running POWER CPUs.

Arguably one of the main factors behind the longevity of the AS/400 platform is the TIMI or Technology Independent Machine Interface which is basically a layer that isolates software from hardware and allows applications to run on any underlying processor. Programs originally written and executed on the older CISC CPUs would also run after the major architecture change (to RISC) which made transitioning to newer machines with far more computing horsepower a relatively painless process. Also this interface should, on paper, allow IBM to adapt to future processor technologies while maintaining full backwards compatibility for legacy applications.

Another key feature is the built in SQL based DB2 Relational Data Base Management System (RDBMS) that is included in the turn-key set of applications along with every program required to run the system. And again, due to the object based architecture, the database performance scales right along with the number of processors in the system.

IBM has re branded the trusted AS/400 platform numerous times throughout its life beginning with the transition to iSeries in 2000, then to i5 in 2004 and currently is sold as System i.

IBMs AS400 (iSeries) homepage