Its the first commercially available virtualization solution I'm aware of. But the terminology for everything prior to the 70s is so different it makes it hard to evaluate the documentation without a really close read

​@@christopherjackson2157A big difference between mainframes and PCs is that hardware functions on mainframes are handled by essentially separate computers running their own firmware (microcode or licensed internal code in IBM-speak). 3270 user terminals would go through a communication controller like the 3174 Establishment Controller. A 3480 tape drive has its own controller box with microprocessor and floppy-loaded firmware. This is the key to the scalability of mainframes. What's relevant is that the operating system on the actual mainframe processor handles very little of the hardware tasks that OS drivers do today. Therefore, the OS is much simpler and virtualization is much simpler. Instead of faking hardware to isolate guests, like PC virtualization has to do, it becomes more of a virtual memory and data routing problem. The guest OS, CMS, is a very lightweight single-user OS. It's more complex to run multiple instances of MS-DOS prompts under Windows 3.1, which used virtual machine techniques to get real-mode MS-DOS programs to multitask in a 386 environment. To that extent, the 286/386 virtual memory system was referred to as virtual machines through the early 90's. Like they talk about here, each process has its own address space that's completely independent from other processes, and the OS manages hardware. The motivation of modern PC virtualization is that the OS itself (what they call the control program here) got so complex and services provided got so intertwined between processes, we have to add another layer and run multiple OSes.

@@christopherjackson2157had Burroughs not a comparable solution? They were the first with the virtual memory, so maybe they were earlier, but maybe not as transparent and thought out as IBM.