AS400 vs iSeries vs System i
AS400, iSeries, and System i are not separate product families. They are successive IBM brand names for the same platform lineage that now continues as IBM i on IBM Power Systems hardware.
AS400, iSeries, and System i describe different branding eras of the same IBM mid-range platform lineage. They are not three unrelated systems. IBM changed the product name over time while keeping the core operating environment, application model, and upgrade path connected.
The Simple Answer
If a company says it runs AS400, iSeries, or System i, it is usually talking about the same family of workloads. The business may be referring to the original AS/400 hardware, a later iSeries or System i generation, or a current IBM i environment that still inherits the same platform identity.
The differences are mostly about branding period, hardware generation, and official IBM naming at the time the system was purchased or last upgraded.
What Changed at Each Rename
- AS/400: Original brand introduced in 1988, paired with OS/400 and integrated database design
- iSeries: Name adopted in 2000 during IBM's e-business branding period
- System i: Name adopted in 2006 when IBM unified server branding under System families
- IBM i: Current operating system name since 2008, running on IBM Power Systems hardware
Each stage brought newer hardware and updated IBM branding, but not a break in application compatibility or platform identity. That continuity is why older RPG and COBOL workloads can still run on current IBM i environments.
Where IBM i Fits In
IBM i is the current operating system name. That makes it different from AS400, iSeries, and System i, which were used as overall platform or hardware-era brand names. Today the more precise way to describe the environment is:
- IBM i: the operating system
- IBM Power Systems: the hardware family
- AS400: the legacy market term many users still apply to the whole platform
If you need the current official terminology for an upgrade project or vendor discussion, IBM i plus IBM Power Systems is the cleanest wording.
Which Term Should You Use?
Use AS400 when matching legacy search behavior or discussing the historical brand. Use iSeries or System i when describing a specific generation of hardware or an older installed environment. Use IBM i and IBM Power Systems when documenting the current platform precisely.
For a broader naming walkthrough, see What Replaced AS400? and AS400 History Timeline.