AS400 Learning Center

What Replaced AS400?

IBM i on IBM Power Systems hardware replaced the AS400. The operating system evolved through iSeries, System i, and IBM i naming. IBM Power10 and Power11 are the current hardware generation. The workloads never disappeared ... only the brand names changed.

Nothing replaced AS400 in the sense of a foreign platform taking over. IBM itself renamed and evolved the platform. The AS400 became the iSeries, then the System i, and is now officially called IBM i running on IBM Power Systems hardware. Organizations that say they are still running AS400 are running the same lineage of platform, evolved over four decades, still managed by IBM.

The Official Naming Sequence

IBM renamed the platform in stages, each reflecting a broader branding strategy:

  • AS/400 (1988-2000): Application System/400. Original hardware and OS. The OS was called OS/400.
  • iSeries (2000-2006): Rebranded during IBM's e-business era. The OS became i5/OS on the iSeries 400, 800, 810, 820, 825, 830, 840, 870, 890 models.
  • System i (2006-2008): IBM unified its server branding under System i, System p, System x, and System z.
  • IBM i (2008-present): IBM separated the OS name from the hardware name. IBM i became the OS. Power Systems became the hardware. IBM i 7.1 through 7.5 covers the current release history.

What Is IBM i Running On Today?

IBM i runs on IBM Power Systems hardware. The current hardware generations in production are:

  • IBM Power9: Released 2017, still in many active environments, approaching end of mainstream support
  • IBM Power10: Released 2021, current workhorse generation for most upgrade projects
  • IBM Power11: Released 2024, the current flagship, with new performance and efficiency characteristics

IBM i is designed to run on IBM Power hardware and only IBM Power hardware. It does not run on x86 servers or cloud infrastructure natively, though LPAR virtualization and IBM Power on-demand options exist.

Did Anything Compete With AS400?

AS400's primary competitors in the mid-range space were Digital Equipment Corporation's VAX/VMS, Hewlett-Packard's HP-UX systems, and Sun Microsystems' SPARC/Solaris line. All of those platforms either died or became marginal. The AS400 lineage ... now IBM i ... outlasted all of them.

In the broader market, x86 Linux and Windows servers absorbed significant mid-market share through the 1990s and 2000s. But for the specific workloads AS400 dominated ... vertically integrated ERP, high-transaction database, and always-on business processing ... the IBM i platform maintained its position.

Should You Migrate Off IBM i?

This depends on your specific situation, not on the platform's viability. IBM i is not a platform in decline. IBM Power11 delivers new performance capabilities, and IBM i 7.5 continues to receive feature updates.

Reasons to consider migration: lack of internal IBM i skills, inability to find RPG developers, business applications with no IBM i ISV path forward, or acquisition scenarios where the parent company standardizes on a different platform.

Reasons to stay: stable workloads, IBM Power performance advantages for database-heavy processing, existing code investment, IBM i reliability history, and lower long-term operational cost for mature environments.

Frequently Asked Questions

Was AS400 discontinued?
No. IBM evolved and rebranded the platform, but never discontinued it. The AS400 became iSeries, then System i, then IBM i. IBM Power Systems replaced the AS400 hardware. The workloads, the OS lineage, and IBM's investment in the platform have continued uninterrupted.
What is the newest version of AS400?
IBM i 7.5 is the current OS release (as of 2022). IBM Power11 is the current hardware generation (as of 2024). Together, they represent what would have been called the latest AS400 if IBM had not renamed the platform.
What is the difference between iSeries and AS400?
iSeries was the brand name IBM gave to AS400 hardware in 2000. The iSeries ran i5/OS (the renamed OS/400). Functionally, iSeries was AS400 under a new name, with updated hardware models. Both terms now colloquially refer to the same IBM midrange platform lineage.