I wish there was a way to learn mainframes that were accessible to mere mortals. Some toying around with a (almost certainly illicit) emulated copy of z/OS reve

I wish there was a way to learn mainframes that were accessible to mere mortals. Some toying around with a (almost certainly illicit) emulated copy of z/OS revealed an extremely complex, no doubt powerful, but entirely alien system that I'd have loved to get my head around, but alas, I could find no good resources.