5 ms·

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

by tbodt 6y ago

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.

userbinator 6y ago
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.
- quietbritishjim 6y ago
  Here's a bit more detail from The Old New Thing blog about Windows 3.11: https://devblogs.microsoft.com/oldnewthing/20100517-00/?p=14013 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.
  - quietbritishjim 6y ago
    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=24063 https://devblogs.microsoft.com/oldnewthing/20071224-00/?p=24...

by tbodt 6y ago

userbinator 6y ago

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.

quietbritishjim 6y ago
Here's a bit more detail from The Old New Thing blog about Windows 3.11: https://devblogs.microsoft.com/oldnewthing/20100517-00/?p=14013 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.
- quietbritishjim 6y ago
  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=24063 https://devblogs.microsoft.com/oldnewthing/20071224-00/?p=24...