Typical of IBM branding, their naming makes no sense and everyone still uses AS/400 to refer to IBM i.
So here's is what I have been able to discern,
Operating System
IBM i refers to the operating system formally called,
- OS/400 (original name)
- i5/OS (introduced in 1999 with LPARS)
The most versions of IBM i released,
- 5.4
- 6.1
- 7.1
Hardware
In their marketing wisdom, IBM decided to name the hardware platform IBM System i formally called,
- AS/400 (originally name introduced in 1988)
- eServer iSeries (in 2000)
- System i (in 2006)
And to make things more confusing in 2008, the platform was merged with the System p platform (which ran AIX and Linux) into IBM Power Systems.
Confused yet? Even IBM is by their website. Today, many people still refer to the hardware and software as AS/400 or iSeries.
Nutshell
So in a nutshell, the OS is IBM i and the Hardware Platform is IBM Power Systems which can run in LPARs,
- IBM i (various versions 6.1 and 7.1)
- Linux (Redhat, hopefully Ubuntu some time)
- AIX
So Which Operating System is the Host?
I still don't know which OS is the host OS yet.