And the second The Old New Thing story, about adding a Windows 3.1 virtual machine to Windows 95.
As the Windows 95 project started to come together, I was approached to undertake a special project: Run Windows 3.1 in an MS-DOS virtual machine inside Windows 95.
This was the ultimate in backward compatibility, along multiple axes.
First of all, it was a demonstration of Windows 95’s backward compatibility by showing that it could even use an emulated MS-DOS virtual machine to run the operating system it was designed to replace.
Second, it was the ultimate backward compatibility ripcord. If you had a program that simply wouldn’t work with Windows 95 for whatever reason, you could fire up a copy of Windows 3.1 in a virtual machine and run the program there.
To use it, you installed Windows 3.1 and Windows 95 into separate directories, and then made a few edits to the Windows 3.1 SYSTEM.INI file to replace the mouse and serial drivers with special versions. There were some other preparatory steps that had to be done, but eventually you got to the point where you could double-click the Windows 3.1 icon, and up came Windows 3.1 in an MS-DOS virtual machine.
This is quite similar to how Windows 3.x worked in OS/2 at the time.