I started my career as an operations analyst. Worked my way up to be a systems programmer for MVS. During my career as a systems programmer, I wrote several assembler programs on MVS. Those were interesting days and nights.
I was actually surprised to know that I can install MVS on my PC. The same version of MVS I supported - MVS 3.8! I know, it's not state of the art. It's just 24 bit addressing! But I think it is a good tool if one wishes to learn about operating systems in general and MVS in particular. Or if one just wants to relive old glory days in writing assembler code.