AS400 vs IBM i: One Platform Lineage, Different Jobs
AS400 names the original platform and remains common shorthand. IBM i names the current operating system. IBM Power names the current hardware that runs it.
AS400 and IBM i belong to the same platform lineage, but they do not name the same thing. AS400 was IBM's original system brand. IBM i is the current operating system, and IBM Power is the current hardware.
The Short AS400 vs IBM i Answer
Use AS400 when you mean the legacy platform name or the broad term a team uses for its environment. Use IBM i when you mean the operating system. Use IBM Power when you mean the current server hardware.
People will still understand AS400 in ordinary conversation. Precision matters when a release number, contract, software requirement, or machine model controls the decision.
What Each IBM Platform Name Actually Does
| Name | What it names | How it is used today |
|---|---|---|
| AS/400 or AS400 | The Application System/400 platform IBM introduced in 1988 | Legacy brand and common shorthand for the wider environment |
| OS/400 | The original AS400 operating system | Historical operating-system name |
| iSeries | The server brand that followed AS400 in 2000 | Legacy hardware-era name |
| System i | The server brand used before IBM Power Systems | Legacy hardware-era name |
| IBM i | The operating system that evolved from OS/400 | Current operating-system name |
| IBM Power | The current server family | Hardware that can run IBM i, AIX, or Linux |
Why Teams Still Say AS400
AS400 became the natural name for the whole environment during the years when many companies built their core applications. The name stayed in job titles, vendor descriptions, support tickets, and daily conversation even as IBM changed the product names.
That shorthand is not wrong when everyone understands the context. It becomes too vague when a technical decision depends on whether the subject is the operating system, the server, or the application.
When the AS400 and IBM i Distinction Changes the Decision
| Decision | Name that matters | Why |
|---|---|---|
| Check operating-system support | IBM i release | IBM publishes support dates by IBM i release |
| Check server compatibility | IBM Power machine type and model | Hardware support depends on the exact server and required IBM i level |
| Check application compatibility | IBM i release and application version | The vendor certifies a software combination, not the broad AS400 label |
| Order maintenance | Hardware serial number or software entitlement | The contract must attach to the correct product |
Follow the AS400 Question to the Dominant Answer
For the operating system name and version check, use AS400 OS. For release dates and upgrade steps, use IBM i Release History. For the broader platform definition, use What Is AS400?.
This comparison page keeps the names straight. The linked pages handle the deeper operating-system, release, and platform questions.