Fallout 3 isn't designed for Windows 7 or newer systems
It means the explanation breaks down the concept into simpler parts for clarity.
You need to update it; otherwise it may fail at startup. The fix takes about five minutes.
It works smoothly on Windows 7, 8.1 and 10.
It causes significant issues. It fails on consoles as well. It keeps crashing.
Fun to say, working smoothly on Windows 8.1 is great!