ARPANET (1969)

In 1969 a computer filled a room, cost as much as a building, and only a few universities had one. Researchers in different cities wanted to use each other’s computers without travelling across the country. So they joined them together.

1What ARPANET was

ARPANET

ARPANET stands for Advanced Research Projects Agency Network. It was set up by ARPA, an agency of the US Department of Defense, and started working in 1969. It is the network the Internet grew out of.

Its first job was simple: let researchers at different universities share computers and data. By the end of 1969 it joined four sites:

UCLA

University of California, Los Angeles

SRI

Stanford Research Institute, near San Francisco

UCSB

University of California, Santa Barbara

Utah

University of Utah, Salt Lake City

Here they are, where they really were. Press Play to watch the network grow, or replay its very first message.

ARPANET, 1969 to 1973

Drag sideways to turn the globe. Use the slider to move through the years.

19694 sites on the map

1969 · ARPANET is born. Four university computers in the USA are connected — UCLA, SRI, UCSB and the University of Utah.

Places are shown where they really are. The lines are simplified: they show which places were connected, not the real cable routes.

2The first message was two letters long

On 29 October 1969, a student at UCLA tried to log in to the computer at SRI, about 500 km away. He typed LOGIN. The L arrived. The O arrived. Then SRI’s computer crashed.

So the first message ever sent on ARPANET was LO. An hour later they fixed the fault and the full login went through.

3How it grew

1969

Four sites connected.

1971

Fifteen sites. Ray Tomlinson sends the first email between computers — and picks the @ sign for addresses.

1973

ARPANET crosses the ocean: Norway and London join over a satellite link.

1983

ARPANET switches to TCP/IP — one common set of rules for sending data, still used by the Internet today.

1990

ARPANET is switched off. A newer network, NSFNET, had taken over its work.

Rules for sending data

A set of rules that computers follow to talk to each other is called a protocol, and TCP/IP is one. Protocols have a chapter of their own later in this unit.

4Why more than one path mattered

Look at the 1969 map again. UCLA could reach SRI directly — or through UCSB. That second path is not wasted cable. If one line fails, messages can still get through the other way.

Cut a line

Click a line to cut it (click again to repair). Watch how UCLA's message finds its way — or doesn't.

Send from UCLA to

Straight there: UCLA → SRI.

Now try cutting the line to Utah. Utah had only one line, so one break cuts it off completely. Networks built after ARPANET learned this lesson: important places get more than one path.

5What held ARPANET back

ARPANET was for research paid for by the Department of Defense. Most universities, and everybody else, could not join. As more colleges wanted a network, a bigger and more open one was needed. That network was NSFNET — the next lesson.