The early history of PCM transmission

In the very beginning of the 20th century the first digital transmission systems for halftone pictures had been invented. This first evolution of PCM systems is shown by the development from the patent of E. Fortong to the first implementation of an analog-to-digital converter by A. Korn and to commercial picture transmission over atlantic cables by M. D. McFarlane. Finally, the development of the PCM transmission of telephone signals more than 30 years later is shortly mentioned.