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Jack Woehr

Dr. Dobb's Bloggers

Closed Open Source Community

September 26, 2008

Anyone who doesn't believe that Mainframing has drama and pathos should read Melinda Varian's VM and the VM Community: Past, Present, and Future. The author is an esteemed lady programmer present at the creation of VM, or nearly, and later one of the leaders of what you might call a closed open source community of the 1970's and 1980's.

Her 70-page paper, delivered in 1997, is a magnificently written summary of a technical revolution, starting at a time when microcode consisted of wiring embedded in mylar sheets and continuing on into the Internet Age.

It's a story of great beauty and great frustration, a sort of Silmarillion of hitech. There are ideals, plans, successes, failures, betrayals, and no shortage of broadly humorous elements, such as the depths of duplicity managers went to in order to conceal the work they were doing on a project that higher-ups would have killed in a moment had they been told frankly what were the intentions of the development team.

VM was the IBM techie answer to IBM's mangement-designed TSS, which sank without a trace about the time Unix was invented. VM's hypervisor CP was sold to management as "a debugging tool" for TSS, which it certainly was, and ever so much more. It was an entirely new way to provide very powerful interactive computing for many users and processes at one time.

IBM VM in the 1970's was absolutely the kick-butt development environment of its time, offering a personal mainframe to every user. The design was pleasing orthogonal, the virtual processor was a one-to-one emulation of the real processor, ditto other elements of the model, such as memory, storage and I/O.

This spawned a great deal of creativity. VM'ers had an interactive environment which ran at PC speeds and sported 31-bit memory addressing as well as international networking. Rexx , the Perl of the Mainframe World, was invented on VM.

Importantly, VM was distributed by IBM in source form. That source was guarded by an army of lawyers. The juncture of VM's popularity among the real programmers, complete source availability and legal fu created the closed open source community of which we spoke above.

Ms Varian recounts the experiences of a user community able to share concepts and real code with one another, unable to redistribute modified systems, sometimes able to get IBM to incorporate into VM the best of their ideas, and all the while burning with an artistic and professional passion for the VM environment.

It's one of the classics of our profession, and VM is still a very entertaining programming environment, spilling out of its box as it were in the form of VSAMPI which I'm exploring in PigIron .

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