This has been an ongoing
argument disagreement in our IBM i and RPG programmer communities for well over a decade: Should IBM have changed the name when the launched the replacement for the old AS/400 computer? Many people using the latest IBM i servers still enjoy calling it "the 400" but the big problem with this is that non-technical people (often management) hear this and then think they are still using the huge old fashioned pre-internet computer system of yesteryear.
A simplified history of The 400:
Hardware: The AS400 was a minicomputer system introduced in the 1980's. In the 1990's it was replaced by the iSeries system. In the 2000's the iSeries was replaced by the System i. The System i was replaced by the current IBM Power System.
Software: Operating system has evolved and been rebranded with each new system hardware upgrade -- from OS400, thru I5/OS to the current grandchild of the old OS400 operating system called IBM i.
I like to describe this as: