What's ironic is that the entire point of an OS that supports multiple processes is to provide them each with an illusion that they're totally in control of the

What's ironic is that the entire point of an OS that supports multiple processes is to provide them each with an illusion that they're totally in control of their own machine. This abstraction was kind of leaky -- different processes typically share various namespaces, like filesystems, process tables and user accounts. As a result, virtualizing an entire OS became a way to make a tight abstraction of having an independent machine at your disposal. The reason virtualization happened was because emulating the system hardware was easier than changing every OS to adequately separate their namespaces. Now that virtualization has the attention of OS developers, you have development like LXC / cgroup stuff in Linux, bringing isolation into the OS, where it should have existed all along. AFAIK the mainframe world -- which, by the way, still exists -- has never gotten out of the early-computing mindset of having an expensive machine which must be shared between applications, so isolation and containerization has always been a feature of mainframe OS's.