An anonymous reader quotes a report from Science Magazine: There is no doubt that Sci-Hub, the infamous -- and, according to a U.S. court, illegal -- online repository of pirated research papers, is enormously popular. But just how enormous is its repository? That is the question biodata scientist Daniel Himmelstein at the University of Pennsylvania and colleagues recently set out to answer, after an assist from Sci-Hub. Their findings, published in a preprint on the PeerJ journal site on July 20, indicate that Sci-Hub can instantly provide access to more than two-thirds of all scholarly articles, an amount that Himmelstein says is "even higher" than he anticipated. For research papers protected by a paywall, the study found Sci-Hub's reach is greater still, with instant access to 85% of all papers published in subscription journals. For some major publishers, such as Elsevier, more than 97% of their catalog of journal articles is being stored on Sci-Hub's servers -- meaning they can be accessed there for free. In a chat with ScienceInsider, Himmelstein concludes that the results of his study could mark "the beginning of the end" for paywalled research.