Popularly known as Universal asynchronous receiver-transmitter(UART) is a computer hardware device for asynchronous serial communication in which the transmission data and speed format can be configurable.
The driver circuit handles the electric signaling levels, external to the UART and there are two common signal levels, RS-485, a 5-volt system and a 12-volt system.
For an operator console, teletypewriters used to attach it, as it was one of the earliest computer communication devices. For the internet, one of the interesting facts is that it was also an early hardware system.