AS400 vs IBM i
AS400 is a hardware brand name from 1988. IBM i is the current official name for the operating system that runs on IBM Power hardware. They are the same lineage, different names. Understanding the distinction matters for licensing, support conversations, and upgrade planning.
The short answer: AS400 is a brand name for the original hardware IBM released in 1988. IBM i is the current name for the operating system that evolved from that hardware's OS (OS/400). In casual use, both terms refer to the same IBM midrange platform lineage. In precise technical use, IBM i is the OS and IBM Power Systems is the current hardware. AS400 is legacy terminology that many professionals still use as a generic descriptor.
What Is AS400?
AS400 refers to the IBM Application System/400, a hardware and software platform IBM introduced in 1988. The original AS400 systems ran the OS/400 operating system with the integrated DB2/400 database engine. AS400 was both the hardware model name and the colloquial name for the entire platform including its OS and software ecosystem.
What Is IBM i?
IBM i is the name IBM gave to the operating system that evolved from OS/400 starting in 2008. IBM i 7.1 was the first release under the IBM i name. Current releases are 7.3, 7.4, and 7.5. IBM i runs exclusively on IBM Power Systems hardware. IBM i includes the DB2 for i database engine, the IBM i object storage model, and all the capabilities of the original OS/400 plus decades of additions.
Key Differences: AS400 vs IBM i
| Dimension | AS400 | IBM i |
|---|---|---|
| Era | 1988-2000 | 2008-present |
| Type | Hardware brand name | Operating system name |
| Hardware | AS400 hardware models (9406, etc.) | IBM Power Systems (Power9/10/11) |
| OS | OS/400 | IBM i 7.1 through 7.5 |
| Status | Legacy term, widely used colloquially | Current official IBM designation |
Why Do People Use AS400 Instead of IBM i?
Vocabulary from the platform's dominant era (1988-2000) embedded deeply in organizational culture and job market terminology. RPG developers, system administrators, and IT managers who trained in the 1990s use AS400 as the natural shorthand for the platform. Hiring managers still write job postings for AS400 administrators. Vendors still market AS400-compatible software.
Google search data confirms that AS400 still outperforms IBM i as a search query for most intent categories, including technical support, job listings, hardware comparisons, and software directories.
Does the Distinction Matter Practically?
In most everyday conversations about the platform, the distinction does not matter. When IT teams talk about their AS400 environment, everyone understands they mean IBM i on Power Systems hardware.
The distinction matters when:
- Purchasing licenses or support contracts (IBM uses IBM i and IBM Power naming in contracts)
- Evaluating software compatibility (IBM i release version matters, not AS400 version)
- Comparing end-of-support dates (IBM publishes support dates for IBM i releases, not AS400 releases)
- Hiring talent (job market uses both terms, but the skills are the same)