IBM Power Hardware Center

AS400 Model History

IBM launched the AS/400 in 1988 as a single integrated hardware and software system. The AS400 model line ran for roughly a decade, spanning the original CISC-based systems and the mid-1990s transition to RISC hardware, before the platform was rebranded iSeries in 2000.

The AS/400 (Application System/400) launched in June 1988 as IBM's replacement for the earlier System/36 and System/38 mid-range platforms. Unlike many competitors, IBM designed the AS/400 as a single integrated system: hardware, the OS/400 operating system, and an integrated relational database were built and sold together. The AS400 hardware line ran for about twelve years under that name before IBM renamed the platform iSeries in 2000.

The Original AS/400 (1988)

IBM announced the AS/400 on June 21, 1988, positioning it as a single-system replacement for both the System/36 (aimed at smaller businesses) and the System/38 (aimed at larger, more technical shops). The original AS/400 models were built around IBM's proprietary CISC processor architecture and IMPI (Internal Microprogrammed Interface) instruction set. Early AS/400 systems were commonly referenced by model numbers in the 94xx range, including the 9401, 9402, 9404, 9406, 9407, and 9408, with configurations scaled by processor feature and memory size rather than by a large number of distinct chassis designs.

The CISC-to-RISC Transition (1995)

In 1995, IBM moved the AS/400 line from its original CISC architecture to a RISC architecture based on the PowerPC-AS processor family, a variant of the same POWER lineage that underpins today's IBM Power Systems hardware. This was a significant technical shift: IBM re-engineered OS/400 so that existing customer applications, largely written in RPG and COBOL, could migrate to the new RISC hardware without being rewritten, using automatic translation of the machine-independent object code that AS/400 software had always been compiled to. This object-code portability is a large part of why applications written in the 1990s can still run on current IBM i hardware today.

AS/400 Advanced Series

Following the RISC transition, IBM marketed later 1990s AS/400 hardware under the "AS/400 Advanced Series" name, continuing to scale the model line from small entry configurations up through larger multi-processor systems for bigger IBM i (then OS/400) workloads. Performance during this period was measured in CPW, the same Commercial Processing Workload metric IBM still uses to rate current Power hardware, which is why CPW comparisons can, in principle, span all the way from 1990s AS/400 systems to current Power11 hardware.

End of the AS400 Hardware Brand

IBM retired the AS400 hardware brand in October 2000, replacing it with iSeries as part of a broader e-business era rebranding. The underlying architecture and OS/400 software lineage carried forward unchanged in substance; only the brand name changed. This is the first of three rebrandings the platform went through between 2000 and 2008, ending with today's IBM i and IBM Power Systems names. See IBM Power Systems overview for the full naming timeline.

Frequently Asked Questions

When was the AS/400 released?
IBM announced the AS/400 on June 21, 1988, as a replacement for the earlier System/36 and System/38 platforms.
What processor architecture did the original AS/400 use?
The original AS/400, from 1988 to 1995, used IBM's proprietary CISC architecture with the IMPI instruction set. In 1995, IBM moved the platform to a RISC architecture based on the PowerPC-AS processor family.
How did AS/400 applications survive the CISC-to-RISC transition?
AS/400 software was compiled to a machine-independent object code format, not directly to CISC or RISC instructions. When IBM moved to RISC hardware in 1995, existing application object code was automatically translated to run on the new architecture, largely without requiring source code changes.
When did the AS400 name stop being used for new hardware?
IBM retired the AS400 hardware brand in October 2000, replacing it with iSeries. The underlying OS/400 software and system architecture continued forward under the new name.