History of AS400 and IBM Power Systems

The AS/400 name still appears in conversations because the platform lineage has stayed relevant for decades. What changed over time was the product name, the operating system branding, and the hardware family.

The short version

The platform began as the AS/400. Over time IBM renamed and repositioned the system, but the underlying idea stayed the same: a tightly integrated business platform built for reliability, security, and long-term application stability.

Today, the current operating system is IBM i, and the current hardware family is IBM Power.

The major name changes

The names changed as IBM updated the product line:

• AS/400 was the original product name.
• OS/400 became the operating system branding for the original line.
• iSeries reflected a later generation of the same platform family.
• System i continued the branding evolution.
• IBM i is the modern operating system name.
• IBM Power is the current hardware family.

The exact branding changed, but the platform identity remained consistent enough that many teams still call everything “AS400” out of habit.

Why the lineage matters

Understanding the history helps you avoid two common mistakes.

First, it stops you from treating AS400 as if it were a single frozen machine from the 1980s. The platform has changed repeatedly.

Second, it helps you speak precisely about the layer you mean. If you are discussing software behavior, IBM i is the right term. If you are discussing servers, IBM Power is the right term. If you are discussing the platform story people remember, AS400 is still the common shorthand.

What did not change

Several traits have remained consistent across the lineage:

• strong reliability expectations
• integrated database and security concepts
• long application life cycles
• compatibility-focused evolution
• a business-first operating model

That continuity is a major reason the platform still exists in production environments.

Where this fits in the series

This article follows the terminology bridge from the prior article and prepares the reader for the technical explanation later in the series.

If you want the simplest beginner starting point, read What Is AS400 (IBM i)? A Complete Beginner’s Guide.