Microcontroller is a micro computer in an integrated circuit package which contains a microprocessor core, RAM and peripherals. Microcontrollers are processor units aiming at embedded systems. For that reason they are generally used in devices that are automatically controlled. In microcontrollers category Arduino, Raspberry Pi and Adafruit microcontrollers are listed.
Microcontrollers are often compared to microprocessors. The main difference between them is that microcontrollers are aimed at embedded systems. A microprocessor requires external units like RAM, ROM or PIA to work, but microcontrollers have these units embedded, so microcontrollers can run their programs without the need of external components. This feature also allows keeping the project in acceptable sizes. On the other hand microprocessors generally have much more processing power.
The first examples of microcontrollers were intended for industrial use. After the introduction of open source platforms like Arduino and Raspberry Pi, microcontrollers find their way into hobby robotics and electronics. Especially microcontrollers are frequently used in robotic application where sizes and weights are very important.
The first microcontroller is TMS1000 which is developed by TI and released in 1974.