Nowhere, but some people call System I/(A/400)/I-Series a mainframe. It's midrange, but people call it what they call it.

Anyway, IBM i and AIX run on the same hardware. They used to be called System I and System P. Now it's just Power Systems.

Maybe thats what he ment.

Or well, come to think of it. There is a UNIX side to z/OS itself.