I would like to learn how to use a mainframe? does anyone know if any of the mainframe os's (z/os and os/400 off the top of my head) can be run in a virtual env

I would like to learn how to use a mainframe? does anyone know if any of the mainframe os's (z/os and os/400 off the top of my head) can be run in a virtual environment? so I can learn them? as an admin, big iron turns me on :D