JSTOR ( ; short for "Journal Storage") is a digital library founded in 1995. Originally containing digitized back issues of academic journals, it now also includes books and primary sources, and current issues of journals. It provides full-text searches of almost 2,000 journals. As of 2013, more than 8,000 institutions in more than 160 countries had access to JSTOR; most access is by subscription, but some older public domain content is freely available to anyone. JSTOR's revenue was $69 million in 2014. 

William G. Bowen, president of Princeton University from 1972 to 1988, founded JSTOR. JSTOR originally was conceived as a solution to one of the problems faced by libraries, especially research and university libraries, due to the increasing number of academic journals in existence. Most libraries found it prohibitively expensive in terms of cost and space to maintain a comprehensive collection of journals. By digitizing many journal titles, JSTOR allowed libraries to outsource the storage of journals with the confidence that they would remain available long-term. Online access and full-text search ability improved access dramatically. 

Bowen initially considered using CD-ROMs for distribution. However, Ira Fuchs, Princeton University's vice-president for Computing and Information Technology, convinced Bowen that CD-ROM was an increasingly outdated technology and that network distribution could eliminate redundancy and increase accessibility. (For example, all Princeton's administrative and academic buildings were networked by 1989; the student dormitory network was completed in 1994; and campus networks like the one at Princeton were, in turn, linked to larger networks such as BITNET and the Internet.) JSTOR was initiated in 1995 at seven different library sites, and originally encompassed ten economics and history journals. JSTOR access improved based on feedback from its initial sites, and it became a fully searchable index accessible from any ordinary web browser. Special software was put in place to make pictures and graphs clear and readable.
how many institutions?
8,000 institutions