In the late 1960s, the U.S. Department of Defense's Advanced Research Projects Agency, ARPA (later DARPA), began funding the ARPAnet, an experimental wide area computer network that connected important research organizations in the U.S. The original goal of the ARPAnet was to allow government contractors to share expensive or scarce computing resources. From the beginning, however, users of the ARPAnet also used the network for collaboration. This collaboration ranged from sharing files and software and exchanging electronic mail now commonplace to joint development and research using shared remote computers.
The Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite was developed in the early 1980s and quickly became the standard host-networking protocol on the ARPAnet. The inclusion of the protocol suite in the University of California at Berkeley's popular BSD Unix operating system was instrumental in democratizing internetworking. BSD Unix was virtually free to universities. This meant that internetworking and ARPAnet connectivity were suddenly available cheaply to many more organizations than were previously attached to the ARPAnet. Many of the computers being connected to the ARPAnet were being connected to local area networks (LANs), too, and very shortly the other computers on the LANs were communicating via the ARPAnet as well.
The network grew from a handful of hosts to tens of thousands of hosts. The original ARPAnet became the backbone of a confederation of local and regional networks based on TCP/IP, called the Internet.
In 1988, however, DARPA decided the experiment was over. The Department of Defense began dismantling the ARPAnet. Another network, the NSFNET, funded by the National Science Foundation, replaced the ARPAnet as the backbone of the Internet.
In the spring of 1995, the Internet made a transition from using the publicly funded NSFNET as a backbone to using multiple commercial backbones, run by telecommunications companies, such as SBC and Sprint, and long-time commercial internetworking players, such as MFS and UUNET.
Today, the Internet connects millions of hosts around the world. In fact, a significant proportion of the non-PC computers in the world are connected to the Internet. Some commercial backbones carry a volume of several gigabits per second, tens of thousands of times the bandwidth of the original ARPAnet. Tens of millions of people use the network for communication and collaboration daily.