Windows handles this much better than any other OS. The API passes versions (== structure sizes on the calling side), and WinAPI can handle that. As for older

Windows handles this much better than any other OS. The API passes versions (== structure sizes on the calling side), and WinAPI can handle that. As for older Windows systems not being able to load new DLLs, they can; the format hasn't changed in a very long time. I've had experience with installing some DLLs on Windows NT 3.51 and running a modern Firefox, which is about 20 years behind the times.