AS/400, iSeries, and IBM i Naming Explained

Learning Objective

By the end of this lesson, you will be able to explain why the same platform has been called AS/400, iSeries, System i, and IBM i over the years, and recognize that these names refer to the same underlying operating system lineage rather than several unrelated products.

Simple Explanation

If you spend any time around IBM i shops, you will hear people casually mix older and newer names for what is, at its core, the same platform lineage: "the AS/400," "the iSeries box," "System i," and "IBM i" all come up in the same conversation, sometimes from the same person in the same sentence.

That is not sloppy speech. It reflects real history. IBM's midrange business computer line has been rebranded several times since it was first introduced, while carrying forward the same underlying design philosophy: a single, tightly integrated system where the operating system, database, and security model are built to work together rather than assembled from separate products.

A rough timeline helps make sense of the names:

• AS/400 was the original name IBM used when this platform launched. It is still the name many long-time IBM i professionals default to out of habit, and the one most often used informally even today.
• iSeries was introduced later as part of a broader IBM eServer branding effort that also produced names like pSeries and xSeries for other IBM product lines.
• System i followed as IBM continued to revise its server branding strategy across its hardware lineup.
• IBM i is the current name, referring specifically to the operating system itself, and is the term used throughout this platform today.

The important thing to hold onto is continuity, not confusion: a program written for what was called an AS/400 decades ago can, in many cases, still run in a modern IBM i environment. The naming changed; the underlying design and much of the compatibility promise did not.

Why It Matters

Understanding this naming history helps you make sense of real conversations, documentation, job postings, and legacy systems you will encounter. A job listing that says "5+ years of AS/400 experience" and one that says "IBM i developer" are very often describing the same skill set. Without this context, you might assume these are different platforms or wonder if your skills from one "version" transfer to another. They do, because it is the same lineage under different names at different points in time.

Practical Example

Imagine a company that has run its inventory management software on this platform since the 1990s. Over the decades, they upgraded their hardware and operating system versions multiple times: what started as an AS/400 became an iSeries machine, then a System i, and today runs as IBM i on modern Power hardware.

Their core RPG programs, written decades ago, still run today with little or no modification, because IBM has prioritized this kind of long-term compatibility across every rebrand. A new developer joining this company might hear the system called "the AS/400" by veteran staff, see "IBM i" in current documentation, and find "iSeries" referenced in older internal wiki pages, all describing the exact same production system. This is a simplified, illustrative example rather than a real company, but it reflects a pattern that is common across long-running IBM i shops.

Common Confusions

"Are AS/400, iSeries, and IBM i different products I need to learn separately?" No. They are different names IBM has used for the same platform lineage over time. The underlying operating system concepts you learn as "IBM i" apply directly to systems people still call an AS/400 or an iSeries.

"Is one of these names more correct than the others?" "IBM i" is the current, official name for the operating system. But "AS/400" remains extremely common in everyday speech, job titles, and older documentation, so recognizing it is just as important as knowing the current name.

"Does the hardware also get called by these names?" Yes, informally. People often use "AS/400" or "iSeries" to refer to the physical machine as well as the operating system running on it, even though strictly speaking IBM i is the operating system and Power Systems is the current hardware line it runs on.

Quick Recap

• AS/400, iSeries, System i, and IBM i are sequential names IBM has used for the same platform lineage, not separate, unrelated products.
• AS/400 was the original name; iSeries and System i followed as part of later IBM branding changes; IBM i is the current name for the operating system.
• Long-term compatibility across these renamings is a deliberate design priority, which is why decades-old programs often still run today.
• Recognizing all of these names helps you understand documentation, job postings, and conversations with experienced IBM i professionals.

Try Asking the AI Tutor

Use the AI Tutor to ask follow-up questions about this lesson. For example, try asking:

• "If AS/400 and IBM i are the same platform, why do people still call it AS/400?"
• "What is Power Systems, and how does it relate to IBM i?"