A lot of people are talking about 50 years like it was a super long time, and propose solutions that are really intended for hundreds to thousands of years. I t

A lot of people are talking about 50 years like it was a super long time, and propose solutions that are really intended for hundreds to thousands of years. I think it's overkill. [Also I think a lot of you are under 30 :-) ] For only 50 years, I'd probably risk making many thousands of DVDs and CDs, using different manufacturers and drives. Store with tons of redundancy and ECC, don't use inner / outer tracks for anything important, etc. Also, are all of the data equally important? You can afford to store the more critical pieces in more expensive and less compact, but more robust formats. I think the real enemy is obsolescence, and that keeping the data simple (and providing decompression programs and indices in easily understandable formats) is likely more important than worrying about bit-dropout, which seems largely manageable over your specified time. For 500 years, I'd print it, or micro-inscribe it. (One problem with printed matter is that it has other inherent value, e.g., fuel for heating the yurts of cold barbarians). For 5K years, micro-inscription and (if you are worried about technological crashes) an archive in the sky. You could populate a host of satellites in various orbits, timed to re-enter at intervals of (say) a decade over a few thousand years (hard to be exact with atmospheric drag and climate change, but you get my drift). Getting something from orbit down to the ground is not hard, getting /noticed/ and picked up as an interesting artifact is probably harder. For 5M years, add a metric buttload of ECC and stick it in the DNA of some critter that doesn't get out much. A bottom-feeder in a radiation-shielded environment would be cool. Say, a lobster.