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VM on IBM mainframes

You are correct about the mainframe statement. It has offered both OS and memory virtualization. It's been a long, long time since I've been on a mainframe but they used virtualize many copies of MVS/TSO and they called them guests. You could also log into a product called VM but I was never certain about the relationship of VM and MVS/TSO. I know that I used to use an e-mail product called PROFS (Professional Office System???) in VM but all of our business work was performed in MVS.

Yes, IBM has had the Virtual Machine product since the early 1970s. Note that it's Machine, not Memory. It grew out of the failed Multics project, which also gave birth to Unix! Anyway, with VM the hardware hosts multiple virtual System 370s, each appearing to be a complete machine with disk, printers, etc., under the control of "CP" which emulates the S/370's control panel switches and such. Users boot some operating system on this "bare machine", usually CMS (Conversational Monitor System), but MVS (and its interactive extension, TSO) and Unix can also be booted, among others.

With the advent of AIX, Linux, and other Unices, I'm not sure what the fate of VM is. It's a fairly decent standalone system, until you want to talk to another user! You find out that the walls between users are quite high, and ways to share disks and process information were always quite kludgey. The MVS people were constantly agitating to have the VM product withdrawn. Legend has it that they made the pitch to yet another IBM president one day. A bit later, while reviewing their development process, he asked them how they did development work. "We run MVS under VM," came the reply, and VM was saved.

VM (with CMS) and MVS (with TSO) are two completely different animals, although as I mentioned above, MVS can run under VM. PROFS (the email and calendaring PRofessional OFfice System that tripped up Ollie North) ran under VM. VM is oriented towards interactive work, while MVS is basically batch (TSO, the Time Sharing Option, is a miserable excuse of a system).

Phil, ex-Beamer

Posted by: Colonel Panijk   Posted on: 04/03/06 You are currently: a Guest | Members login | Terms of Use

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