While searching for reference materials to refresh my memory (I'm actually a high-end techie mainframer), I stumbled across an amazing find - Hercules Mainframe Emulator!
This emulator is free as well as several older IBM OS's (links provided). Apparently, the creators of this project got official approval from IBM to allow downloads of a few (ref. links), considering them to be useless now (scrap-heap mainframes). It even has several variations of CKD DASD that can be emulated. (note - FBA DASD was the first to use Fixed Blocks of 512 bytes, hence FBA). The only hitch is you need TN3270 Emulation for the Console (may cost you around 20USD; didn't find any free, but several 30-day trial).
I haven't yet tried it out since I haven't yet reassembled my secondary/backup PC. It may be something worthwhile to any old-timers like me to have your own personal mainframe OS.
As far as I can tell, only older OS's are obtainable and not any other software (e.g. compilers, applications, etc.). But unless my memory is totally gone, the Assembler has to be there somewhere, otherwise you wouldn't be able to "put together" your OS.
Why would I post this? Maybe just nostalgia. If you note some of the MiPs, it apparently runs amazingly fast compared to the old IBM360's.
Shades of Gray Hair! This may jog my Systems Installation memory (went south when I had to switch from DOS All-In-All to OS Applications-Only)!
Check it out, if for no other reason, funsies. After all, where would MS be if not for good-old Big Blue?
Edit - Forgot to mention that several Mainframe distributions of Linux are also available.
Update - here is a free TN3270 (recommended) using Cygwin on Windows -
Update2 - here is a complete set of instructions -
I may update this occasionally for posterity (if nobody minds).
Edited by submix8c, 26 February 2009 - 01:12 PM.