Ask HN: What's the most stable form of digital storage?

I wrote a program which I'm proud of having done and would like to keep it for posterity. What's a good storage medium where I can keep and load again in the future? Requirements are: size < 1GB, must keep for at least 3 decades, must be easily transportable (for moves between houses and such) and can sit on a shelf. Bonus points for suggestions on an equally stable storage type that some computer will still be able to understand in the future.