In the late 1960s, the Defense Advanced Research Projects Agency (DARPA) of the United States Department of Defense initiated a project to interconnect computers. A small network was created that interconnected four computers, resulting in the creation of ARPANET. Colleges, universities, businesses, government offices, and military installations slowly began gaining access to ARPANET, and two large-scale communication backbone networks developed:

• the INTERNET for use by the government, colleges, and businesses; and

• the MILNET for exclusive military use.

DARPA created a layered protocol stack in which each layer operates independently according to a set of prescribed rules known as Requests for Comments (RFCs) and Military Standards (MILSTDs). These are maintained and updated by the Department of Defense National Information Center (NIC) and the Internet Advisory Board (IAB).

Since its creation, the Transmission Control Protocol/Internet Protocol (TCP/IP) has been widely adopted as a standard in commercial applications, office automation, and personal computing networks. A copy of TCP/IP is integrated into the Berkeley UNIX Operating System, making TCP/IP the common protocol among UNIX systems.