Historically used for many different purposes, thanks to the simplicity of its asynchronous nature, UART dates back to the origins of computing, and it is still a very popular circuit used in many contexts. Personal computers up to the early 2000s included at least one RS-232 serial port, realized with a UART controller and the transceivers allowing to operate at higher voltages. Nowadays, USB has replaced serial communication on personal computers, but host computers can still access TTL serial buses using USB-UART peripherals. Microcontrollers have one or more pairs of pins that can be associated with an internal UART controller, and connected to a serial bus to configure a bidirectional, asynchronous, full-duplex communication channel toward a device connected to the same bus.