Yes. Everything old is new again, it seems. Many old OSes were VM hypervisors in today's parlance--- VM/370 comes to mind; several of the first Unix and other s

Yes. Everything old is new again, it seems. Many old OSes were VM hypervisors in today's parlance--- VM/370 comes to mind; several of the first Unix and other systems I got to play with were virtual machines running on IBM big iron--- and it was also reasonably common to run programs directly in the VM without a guest OS. When I was in school, a common formalism for talking about operating system design was that they provided a virtual machine abstraction to each process. As time went on the "devices" looked less and less like actual hardware devices, so instead of having an emulated punchcard reader and emulated interrupts, you'd have a read(2) syscall. But that's a relatively unimportant detail. And with paravirtualization the cycle continues: the abstraction the guest sees is no longer that of a bare metal machine, but one with an increasing number of syscall-like hypervisor calls...