UNIX achieved its widespread propagation, its penetration of the UNIX history university domain, and its reach into research and industry due to its early dissemination by AT&T to all interested parties at almost no cost and as source code. UNIX''s present functionality emanated not just from AT&T developers but also from external developers who used the product and contributed their own further developments, which they then put at AT&T''s disposal. (Consider the contributions of the University of California at Berkeley, for example.) With the rising commercialization of UNIX by AT&T (now by Novell) since 1983, such creative and cooperative further development became increasingly restricted, and UNIX source code today has become unaffordably expensive and scarcely accessible. Linux provides interested computer scientists and us"ers with a system that revives the old UNIX tradition: Linux is available for free, and everyone is heartily invited (but not obliged) to free & participatory contribute to its further development. Since Linux runs on PC systems, it has begun to penetrate the workrooms of many computer science students and computer freaks.
