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Maybe you spent too much if it was just for hobbyist use.

IBM had classic compilers and OS they just "threw out there" (no license, just included), you can even legally download (see left menu) them today and run on Hercules emulator on your PC. In the 1980s, there were ms-dos shareware IBM mainframe OS (evolved in Z/OS) and DOS (evolved into Z/VSE)environment emulations that had COBOL and 370 assembler, I wrote and ran there on my PC-AT and uploaded to 4381 when good (and later Amdahl). I did buy Turbo Pascal and Prolog but had free/shareware FORTRAN, C, Pascal, LISP compilers too (now somewhere in a rubbermaid tub on 5.25" disk). those wares are still on the web too.

By the early 90s, I was mainly on Unix workstations, and used GCC and gas (GNU assembler). So when I did run into Java at new job, I was not surprised to have free compiler (only peeve was that were was no source code)

VM/CMS is very much alive and well, thank you. It is now known as z/VM and runs on the IBM z series mainframes ...

http://www.vm.ibm.com/

You can even run Linux in z/VM virtual machines now as well as CMS.

There is an emulator available, called Hercules ...

http://www.hercules-390.org/

And an old VM/CMS is available for free, with source ...

http://www.cbttape.org/vm6.htm

Amazingly nobody mentioned OS/360 released by IBM exactly 40 years ago http://ldworen.net/fun/os360obit.html and still downloadable from http://www.cbttape.org/os360.htm

I recall the huge uproar when IBM decided to withdraw access to the source. It was called their "Object Code Only" (OCO) policy and users were outraged. I still have some of the coke can wrappers passed out at a users group meeting making fun simultaneously of OCO and New Coke. (From a Google search, found this which references Feb. 8th, 1983 as the date of the OCO announcement.

There was a very active community within the major IBM users groups such as SHARE, sharing modifications to the systems. The best collection at the time was the CBT Mods Tape which was originally assembled by a Systems Programmer at Connecticut Bank and Trust. I guess it doesn't suprise me that it still exists (Thanks Google!) as it was an invaluable tool back when I was still involved with mainframes.

Cbttape.org is the mainframe version of open-source, but without any GPL license nonsense. We share freely or not at all!

There is a cookbook installation version with a step-by-step guide for neophytes - the MVS 3.8 Turnkey CD - follow the Voelker Bandke link.

As others have noted, the biggest hurdle is that there's no good way for an interested geek to learn firsthand about mainframe systems and OSes. While Hercules takes care of the hardware, at least enough for people to run something to learn on, the same isn't true for the operating system. Modern IBM OSes are hideously expensive, for an individual (unless you're Bill the Gates), and there's been some persistent comments that they won't license them on Hercules anyway (although I have no direct knowledge of this, either way).

I've been advocating a hobbyist license for IBM OSes for use by individuals with Hercules for some time now. There's a white paper at http://www.conmicro.cx/ibmhobbyistlic.html. Aside from a few curmudgeons, and aside from the folks at IBM who make the decisions, the reaction I've gotten to this paper has been uniformly positive. I believe that it would help slow the slide, at least.

In the meantime, the interested can get a running copy of the last public-domain version of MVS from the CBT Tape web page, which is a great resource for the mainframe community in general.

A hint to the coders out there: the number of people who know and understand these systems is declining. There's a mint to be made if you can deliver services to support them.

There is also the issue of the aging of the pool of experienced mainframers. Training (for example) an IBM systems programmer isn't something done at the drop of a hat. It takes time and someone with the experience and knowledge to do the job well, and a fair number of these people will be retiring someday soon.

Fortunately, IBM is pretty good at maintaining backwards compatibility so skills learned on older versions of IBM's mainframe operating systems generally transfer pretty well to the newer versions. Fortunately for someone wishing to dip a toe into the IBM mainframe world there are (apparently) public domain versions of older IBM mainframe operating systems available. I use the weasel "apparently" because I'm not aware that IBM has officially declared these versions to be in the public domain, but they are devoid of copyright statements and unlicensed.

Now here's the beauty part: a group of retro-computing enthusiasts has resurrected these old public domain IBM mainframe operating systems and run them under the Hercules mainframe emulator under Linux, Windows and a few other platforms. Public domain versions of MVS, DOS/VS, and VM are available from the late 1970s/early 1980s. A turnkey MVS system from this era is available, which gives you a running MVS system capable of doing some fairly useful work. Many people have contributed their efforts to providing various MVS tools, and the historical archives at CBT tape have proven a real treasure-trove of goodies just waiting to be rediscovered. Most of the CBT tape offerings include source code, providing a tremendous learning opportunity.

You can also get a CD-ROM with the OS/360 distribution, as well as the public-domain versions of MVS 3.8, VM/370 r6, and other goodies from the CBT Tape Project.

Here is what I did when I got fed up with the junk that passes for computing these days. Get the Hercules IBM 360/370 emulator from here, VM/370 from here or MVS from here and go back to the days of using a real computer!

Here is what I did when I got fed up with the junk that passes for computing these days. Get the Hercules IBM 360/370 emulator from here, VM/370 from here or MVS from here and go back to the days of using a real computer!