Sunday, January 10, 2016

Videotex and Teletext

Laserdiscs controlled by computers were one of the new technologies in the magazines from the 80's. Another one that people were talking a lot was Videotex. End of 70's and beginning of 80's the Videotex were the connected future, together with the Laserdisc, they were knewn as "New Media".

The Networks before Internet

People would read magazines, check their bank accounts, buy show tickets, talk with each other and many other activities, using the network!! If you think that Videotex looks like the Internet, you made a good guess. It looks like Internet but Videotex networks are closed networks. Each network were isolated from the others, only those approved by the network owner can publish contents and only network customers can consume this content. And the Videotex systems from each telecom were different from the others, so a NAPLPS terminal couldn't show pages made for CAPTAIN.

Even with those characteristics that now we see like big problems, many videotex networks were still working until after the 2000's, the biggest one, called Minitel, was shutdown in France only in 2012.

The system created to the Japan by NTT was called CAPTAIN ("Character and Pattern Access Information Network") it was a bit different than the other Videotex systems because it needs to handle the characters of Japanese language, so instead of using graphic primitives (like NAPLPS) or semi-graphical characters (like Prestel), the CAPTAIN system sends the page image pre-rendered to the decoders.

NTT advertising showing many pages as a example of what you can do with CAPTAIN

As a new computer standard, the MSX couldn't be out of Videotex revolution. Sanyo made a CAPTAIN adapter for MSX1 (which include a special graphics adapter because CAPTAIN minimum resolution is 248x204, 12 lines more than what MSX1's VDP can do), Yamaha did a CAPTAIN adapter for MSX2 (an easier job as the MSX2's VDP can reach a not-interlaced resolution of  512x212) and NTT did the NTT CAPTAIN Multi-Station.

The green box talks about Yamaha CAPTAIN adapter

I guess that other countries with MSX computers and Videotex systems had some adapter to connect MSX to Videotex. In Brazil, you could buy a modem cartridge (from any of the many manufacturers) and connect your MSX to "Videotexto", the Telesp (one of Brazilian telecoms) bought many Gradiente Expert with modem cartridges and lease them to their customers to serve as Videotex terminals.

Some cartridges to connect the MSX to "Videotexto": a modem from Gradiente and two RS-232C interfaces from Sharp and Cybertron
(pictures from retroplayerbrazil and from a MercadoLivre auction)

So, to use a Videotex network, you needed to be a subscriber, to have a phone line and a compatible terminal. That compatible terminal could be a dedicated one (like NTT CAPTAIN Multi-Station) or a generic home computer with a modem, the software and the graphical capabilities to show your Videotex system screens (like a home computer + Videotex adapter).

Teletext, the Videotex system of Television Broadcasters

To be fair, the Teletext is older than Videotex. It was created by BBC and used the interval between TV frames to send data. But it's an one way communication: the TV repeatedly sends the data frames in a carrousel: first the weather frame, then the national news, then the calendar, then public advisories, and when it reaches the end, goes to beginning with the weather.

You use your remote to select (through a menu) what you want to see, and when that screen was broadcasted your Teletext decoder shows it on screen. So it looks like you are requesting the information that you want to see. That illusion was even better if your decoder have a lot of RAM, so it can cache many screens and you can see then just after selected at menu. These traditional teletext services are being shutdown as analog transmissions are coming to an end.

Well, back to the history, British Telecom was creating their Videotex system, and did want to send data through phone lines and show the received information on TV screen, more or less the same that BBC was doing. As videotex and teletext wanted to share the output media (the TV set), in 1976, both agreed in a shared output format, so the manufacturers could share components and designs to both systems and, hopefully, bring the prices down.

Learning from british experience, other videotex formats are shared with their teletext equivalents. That's the japanese case, which CAPTAIN format is shared between the Videotex service and the teletext broadcast.

So, that machine makes a lot sense:


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