Virtualisation is a lot older than you might think, with (one of?) the first implementation(s) being IBM’s VM/CMS, the line of operating systems that would grow to include things like System/370, System/390, all the way up until IBM/Z, which is still being developed and sold today; only recently IBM released the IBM z17 and z/OS 3.2, after all.
The VM series of operating systems is designed exclusively for mainframes, and works by giving every user their own dedicated virtual machine running on top of the Control Program, the hypervisor. Inside this virtual machine the user can run a wide variety of operating systems, from the simple, single-user classics like IBM’s Conversational Monitor System, to more complex systems like Linux or AIX.
Early versions of VM were released as open source and are now in the public domain, and enthusiasts have continued to build upon it and expand it, with the latest incarnations being the VM/370 Community Edition releases. They contain the Control Program and Conversational Monitor System, augmented by various fixes, improvements, and other additions. You can run VM in an emulator like Hercules, and continue on from there – but what, exactly, can you do with it?
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