The concept of data communication
The concept of data communication – transmitting data between two different places through an electromagnetic medium such as radio or an electric wire – pre-dates the introduction of the first computers. Such communication systems were typically limited to point-to-point communication between two end devices. Semaphore lines, telegraph systems, and telex machines can be considered early precursors of this kind of communication. The telegraph in the late 19th century was the first fully digital communication system.