I think that title must be given to OS/360. Usable backwards compatibility for half a century, and counting. Windows backwards compatibility took a dramatic tu

I think that title must be given to OS/360. Usable backwards compatibility for half a century, and counting. 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 People had to turn to DOSBox instead, which perhaps ironically was originally made for things like Linux to run DOS software.