The BTX is not strictly a modem or ISDN but is a similar type of device, designed to connect the Amiga to the proprietary German online service called BTX. The cable contains no circuitry but is really just an adaptor from the Amiga's parallel port to the BTX connector adaptor, the real work is done by the Amiga in software. BTX is an acronym for "Bildschirmtext" with means "on screen text" and is a similar technology to "Teletext". UK readers could probably equate BTX with the old service called "Prestel" that used to be supplied by "British Telecom". Later it was renamed to "Datex-J" and was a service provided by the German Post Office since 1984. The service was organised into information pages, most of which were static and contained an internal mailing system for BTX users. Technically a page consists of 40rows and 24lines of pure text with some graphics which was transmitted at 1200baud over a phone line. On the back is a round DIN to connect to a proprietary interface to the users phone line. Two others connect to one or two external monitors. A second monitor was apparantly required by this expensive, unpopular service. The unit was manufactured by Siemens in cooperation with Commodore, and then marketed by Commodore.