IBM i vs AS400 – What’s The Difference? Well, It Depends on Who You Talk To

The purpose of this blog is a light-hearted look at the difference between IBM i and AS400. Also, to underscore that IBM i is a terrific operating system. 

Disclaimed: IBM i is an operating system. AS400 and iSeries are legacy servers. I use these terms interchangeably to make it easier for folks to find this kind of information on the web.

IBM i on POWER has a long successful history and has rightly earned a solid reputation for reliability, excellent support and value.

Clearly IBM i and AS400 (or iSeries) are not the same. IBM i is an operating system that has experienced dramatic enhancement and innovation over the decades. On the other hand, AS400 and iSeries are legacy hardware servers. Even though IBM i is the grandchild of AS400, to compare the two is comparing apples to oranges. There is a BIG difference between IBM i and AS400.

Even so, its users still innocently refer to this fabulous technology as “AS400” or “iSeries”.

While IBM i purists insist we refer to it as “IBM i”, most of the folks I talk to still call it AS400.


First, I think, IBM has done a terrific job to make all of its operating systems and hardware backward compatible so that applications that were originally written for the AS/400 running OS/400 still work on today’s machines. This is a great feature and the strength of the Power Series line. But it also means that certain ways of talking about the technology persist even as the technology changes.

Second, most of the folks I talk to are 55 – 85 years old. They have worked on the platform most of their professional career. They call it what they started with – the older users say AS400, and the younger ones say iSeries.

Why should they change what they call it? They know what they are talking about…so I use their terminology.

It reminds me what Mark Twain once said, “Never try to teach a pig to sing. It wastes your time and annoys the pig.”

Key IBM i Trends

We can expect the POWER server to continue to offer extraordinary performance with a combination of faster processes (POWER10 is clocked at about 16,000 CPW per core) and high-performance, lower-priced SSD drives. We can expect to see a steady reduction in servers in data centers for a significant reduction in performance cost.

The reduction in performance cost also makes IBM i hosting more attractive for users that do not need on-premise computing or prefer to outsource IBM i expertise to manage their IBM i solutions.

IBM i back-compatibility means many applications written for older technology can be migrated forward to new IBM i versions, whether hosted in the cloud or on premise.

When Comparing IBM i to AS400 – Get Ready To Be Thrilled

Quite simply IBM i is way better, faster, and innovative.

When my clients make the leap, they are dazzled.

Need Help?

Call me at 714-593-0387 or email me at Let us know how we can help!

The post IBM i vs AS400 – What’s The Difference? Well, It Depends on Who You Talk To appeared first on Source Data Products.