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Comment by tbodt | Hacker News Reader

Since it's not entirely clear: this works by loading a Linux kernel into unused memory, saving the current state of DOS, turning over control of the computer to Linux, then having the init process start a new that uses the vm86 system call to resume execution of DOS.

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That is actually not far from how the kernel of the Win9x series (and also Win3.x on a 386) is structured --- a "hypervisor"-like kernel runs DOS and Win32 applications in "virtual machines" using the V86 mode of the processor. In Win386/9x, that kernel is known as VMM32. In this case, it's the Linux kernel. It's very interesting to see these "chimeric" OSs appear.

Here's a bit more detail from The Old New Thing blog about Windows 3.11: https://devblogs.microsoft.com/oldnewthing/20100517-00/?p=14...

It includes:

> As you might suspect from its name, the virtual machine manager created virtual machines. Inside the first virtual machine ran a copy of Standard mode Windows. ... The other virtual machines each ran a copy of MS-DOS and were responsible for your MS-DOS sessions. ... It’s kind of stunning to realize that Enhanced mode Windows was really a completely new operating system with multiple virtual machines, pre-emptively multi-tasked with virtual memory.

I think it's quite interesting that, on that version of Windows, all the Windows programs were only cooperatively multitasked while all the DOS programs were pre-emptively multitasked.

By the way, I get the impression that Windows 95 onwards worked a bit differently, with Windows itself more tightly integrated in managing virtual machines rather than running in one itself (more like a type 2 hypervisor). For example, this post seems to suggest that: https://devblogs.microsoft.com/oldnewthing/20071224-00/?p=24...

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