First, a bit of history. In the early 1970s, IBM had two separate operating system development teams competing for the future of the mainframe. The establishment - represented by MVS - offered continuity from the age of the 360.
Another group of trendy virtual machine enthusiasts were quietly working on VM/370 - an exciting route away from the unwieldy monolith that MVS had become. The VM team even had stylish enamel button badges made with the legend "VM Bigot".
Check out the rest here.