The telex, TTY or teletype consists of an alphanumeric mechanical keyboard for writing messages for later sending. It also allows you to receive typed messages from point to point, connects to the end of a telegraph cable for later sending and printing.
It was very popular in the business area for its low cost and legal credibility.
It connects to the end of a telegraph cable for later printing, creating an international network.
The telex, for its better compression, could be assimilated to what we call today “whatsapp”, with the difference that the “whatsapp” is wireless and very high speed.