It depends a lot on the humidity and heat or light in the environment where the microfiche are being stored. But they should be able to retain their data for 500 or so years.

CDs and Laserdiscs are also seeing bitrot. The layer of material that is etched does degrade over time. Error correction helps some, but if it's a writable CD or DVD it's only likely to last a decade or two. M-Drives are CDs that are designed to retain their data for about 1000 years and can be writable by specific consumer drives. Not sure how long the professionally pressed CDs last but it's not that long.

Googling from your comment led to M-Discs, which are available in dvd or blu ray, up to 100gb discs. That looks extremely useful.

ah, thanks for catching the typo, it was getting late for me, I should have pulled up a link or something because I haven't worked with these discs in a decade or so..

yeah those are the ones I'm referring to -- if you're archiving something like family history or data that needs to be good for centuries (without having to re-copy and juggle), those are a better choice than just about anything else.

https://en.wikipedia.org/wiki/M-DISC

What beats M-Disc? Genuinely curious just having bought one.

Nothing comes to mind that you can interface with a computer, but when I wrote the phrase I was thinking of projects on the scale of Long Now [0], requiring physical etching on materials and very careful storage.

Alternatively, tell people that they can't store something and you're likely to find it robustly mirrored by many.

[0] https://longnow.org/ideas/very-long-term-backup/

Well that was a fascinating diversion. This is bonkers!

https://norsam.com/products/buddhist-nano-film/