[OT] paper on Retro ?

Yeah, but I was somewhat disappointed. The cover made it sound like they would discuss *media* that would last a long time, but they were just talking about maintaining the ability for software to handle the data. That's obviously worthwhile, but it's also much easier to figure out: 1) Use industry-standard data formats, not proprietary formats 2) Use text-based formats where possible rather than binary formats 3) Keep a specification for the format along with that data, ideally on the same physical medium 4) Keep the source code for the software that processes the data, ideally on the same physical medium. Ideally use software written in a programming language that is widely used, not something obscure. 5) Keep the tools used to build the binary of the software. etc. On the media side, though, AFAIK there is only one high-density machine-readable media that can be expected with any confidence to last much more than 20 years. That is CD-R with a gold-coated substrate rather than silver or aluminum. Note that gold-tinted dye is NOT sufficient. The main failure mechanism for CD-Rs is oxidation of the reflective layer, and a gold layer won't do that, so then your limit is based on other physical processes that occur even more slowly. Kodak's accelerated aging tests indicated a typical life of several hundred years, so they conservatively claimed one hundred. They used to have a white paper on their web site.