IBM i Chief Architect Steve Will has a post describing the five integral layers of the System i operating system, formerly called i5/OS. They are:
- Integrated Middleware
- “The” Operating System
- Technology Independent Machine Interface
- Licensed Internal Code
Will sums it up at the end:
In summary, the robust IBM i operating system is flexible and long-lived largely due to this layered architecture. When we talk about IBM i, we’re talking about all of these layers in combination. I hope this brief introduction helps you understand the value that comes to you when you run IBM i, and why the IBM i development team continues to work hard to bring you this great integrated operating system.