A substantial fraction of books have been digitized, even if not publicly available. Perhaps a more interesting question would be that of all significant/impor

A substantial fraction of books have been digitized, even if not publicly available. Perhaps a more interesting question would be that of all significant/important knowledge in human history. Some information is more important than other; the name of a childless bachelor who lived in a small town 200 years ago is still knowledge, but it isn't helpful for very much.