30 years of TCP-IP-enabled Internet

The switchover is generally known as a ‘flag day’ – ie, a point at which a major system administration change occurs that requires a full restart or conversion of a major body of computer software or computer data.

The ARPANET was the first operational packet switching network and generally acknowledged as the progenitor of the Internet. The network was initially funded by the Advanced Research Projects Agency (ARPA, later DARPA) within the US Department of Defense for use by its projects at universities and research laboratories in the US.

As recently noted in E&T's look back at the technology behind the Cuban Missile Crisis, the concept of a highly resilient internetwork of connected computers had its origins in the perceived need for a communications system that would continue to work following a military emergency. However, the packet switching element of the ARPANET was partly based on work by UK computer scientist Donald Davies and colleagues at the National Physical Laboratory (NPL).

The TCP/IP-enabled ARPANET was largely superseded by NSFNET (National Science Foundation Network) initiatives starting from 1990.

More information at:
http://eandt.theiet.org/magazine/2012/08/chipping-away.cfm

http://www.tcpipguide.com/free/t_TCPIPOverviewandHistory.htm