You were downvoted for saying this, but anybody who has read the Old New Thing blog (https://blogs.msdn.microsoft.com/oldnewthing/) or Raymond Chen's chapter on Windows backwards compatibility (http://ptgmedia.pearsoncmg.com/images/9780321440303/samplech..., PDF) will be both impressed and horrified at the lengths the Windows team went to in order to avoid breaking programs.

Windows backwards compatibility took a dramatic turn for the worse with Windows 7 when they decided to run old software in a VM instead of keeping compatibility. People had to turn to DOSBox instead, which perhaps ironically was originally made for things like Linux to run DOS software.