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The predigital period lasted 28 years from 1937 to 1965. In 1937 Alec Reeves invented the pulse modulations: PAM, PPM and especially PCM. In 1965, Gordon Moore published his famous law, planning a fast development of the Integrated Circuits (ICs). During this predigital period many theoretical and experimental works were carried on. The 1940psilas were the years of intense works on the Communications Theory, which took into account the digital signals. During the 1950psilas numerous radio systems using PAM and PPM modulations were developed. Lastly the TDM patents of 1945, 1958... marked out a long maturating way to the TDM switching. The European engineers took part to these works.