Shannon, the founder of information theory, was born in the United States in 19 16. He studied at the University of Michigan and Massachusetts Institute of Technology, took Boolean algebra classes, and used differential analyzers under the guidance of mathematician Bush, who invented differential analyzers, which made him interested in the analysis of relay circuits. He thinks that the design of these circuits can be realized by symbolic logic, and realizes that the effective mathematical tool for analyzing relays is Boolean algebra. 1938, Shannon published a famous paper "Symbolic Analysis of Relays and Switching Circuits". For the first time, Boolean algebra was used to analyze switching circuits. It was proved that the logical operation of Boolean algebra could be realized by relay circuits, and the electronic circuit design method to realize addition, subtraction, multiplication and division was clearly given. This paper became the beginning of switch circuit theory. Later, Shannon went to work in Bell Laboratories. He further proved that computers can be made of relays or electronic components that can realize Boolean algebraic operations. Shannon's theory also laid the foundation for computers to have logical functions, so that electronic computers can be used for numerical calculation and have various non-numerical application functions, which makes computers widely used in almost any field in the future. Photo fax machine

Photo fax machine is a kind of fax machine, which is used to transmit continuous tone images in all optical density ranges, including black and white, and copy copies that meet certain tone density requirements through photographic records. Photo fax machines are mainly used in news, public security, military, medical and other departments.