ARPANET was the world's first packet switching network, an early predecessor to the Internet. It was operated by the US Defense Department and worked by organising data into packets, formatted blocks of data for computer formats. It was installed at four locations: Stanford Research Institute, UCLA, University of California and University of Utah.
The system allowed people to send messages between users. The right hand image shows a written log of the first message sent via the network, an early form of e-mails. In fact, one of the timelines I was looking at mentioned the Queen sending an email in the 70s, which I thought strange. There is a perception the Internet was invented in the 90s, and in a way it was - the hypertext browser making data accessible from personal computers only came about in the early 1990s.
In actual fact, Teletext was pre-dated by ARPA. Developed in the late 1960s, it came about a decade before teletext was conceived. In 1970, the network went international, with a station in Norway being added along with one in Hawaii.
Around this time, the BBC had developed a close captioning service to be transmitted via televisions. Teletext, which arrived in 1973, broadcast the information for its service in between PAL transmission signals. It does require an encoder, although this became standard in the mid 90s with all televisions being fitted with this as standard. The Internet, as it is known today, would not become widely available and accessible until the 1990s.
Research from Wikipedia and previous blog posts.