The Internet has passed a major milestone in its history, turning 20 on January 1.

It was on January 1 1983 that Internet-forerunner ARPANET (Advanced Research Projects Agency Network) was fully switched to TCP/IP (Transmission Control Protocol/Internet Protocol) by the US Department of Defense.

The transition came after a decade of development work on the new system, which replaced an earlier, clunkier setup, the Network Control Protocol (NCP).

Transition plans for the NCP-to-TCP/IP move were published in 1981 and some administrators began migrating soon after. But New Year's Day 1983 was the deadline, and one quite a few techies found themselves cramming for, according to Bob Braden a member of the original ARPA research group that designed TCP:

He said: "People sometimes question that any geeks would have been in machine rooms on January 1. But believe me, some geeks got very little sleep for a few days. There may still be a few remaining T-shirts that read, 'I Survived the TCP/IP Transition'."

Of course an Internet-like system was up and running long before 1983: Since 1969, researchers had been exchanging data over ARPANET, a system that connected hundreds of host machines at the time of the TCP/IP switchover. But the standardization of TCP/IP laid the groundwork for today's massive, decentralized network.