VTX5000: Part 1 - Prism, Prestel and Teletext

This article is the first part of a series on the Prism VTX5000 modem for the ZX Spectrum, a device that sparked the author's interest in data communications. It covers the historical background of Teletext (Ceefax, Oracle) and its character generator chip, the SAA5050, which defined the blocky visual style. It then discusses Prestel, the UK's first public Viewdata service, as a two-way interactive alternative to broadcast Teletext. The article is part of a project to implement VTX5000 support in a web-based Speccy emulator, making it a technical and historical exploration of vintage computing and telecommunications.