The storage media. We have evidence to support this:
* original paper works from 1000 years ago are insanely rare
* more recent storage media provide much more content
How many digital copies of Beowulf do we have? Millions?
How many paper copies from 1000 years ago? one
how many other works from 1000 years ago do we have zero copies of thanks to paper's fragility and thus don't even know existed? probably a lot
