e site to another.
Separate, secure links among defense research computer centers were also established, and they continue to exist for the transmission of sensitive or classified information. The original intent of ARPANET was to provide for fast transmission of computer information that was related to government research but was not itself classified or sensitive. Thus, the initial ARPANET, like its descendent the Internet, was an open system which new users could join and through which information could flow freely without access or content controls.
Through the 1970s and early 1980s, the growth of ARPANET, and then the Internet, was gradual and largely invisible to those outside the world of researchers and computer specialists. Other government computer centers were added to the network, as were computers of private businesses engaged in governmental research, but the system came to be primarily university-based. Access was limited to individuals associated with institutional computer centers, not by regulation but by the limitations of technology; until about 1980, "computer" was almost synonymous with a large machine, filling a room or an entire building, operated by a staff of specialists. Even among these specialists, such familiar modern usages as e-mail and bulletin-board messages only gradually emerged, since the software necessary for these applications was a rather late development of technology.
No precise date can be given to the transformation of the Internet into a service available to a broad public, but the decisive factor in the transformation was the development and popularization of the personal computer. Once personal computers became fairly popular, at least among students and researchers, it was natural for individual university and other computer centers to provide for personal-computer access, by modem and phone line, to their own internal networks. Users of these internal networks in tur...