The telex, TTY or teletype is a device similar to a typewriter. It has an alphanumeric keypad that manages to compose messages that can be sent at that moment and receive a response as if it were a written dialogue or be perforated in a tape to be transmitted in seconds and consequently wait for the response.
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.