The microcontroller is essentially a computer on a chip. It contains a processing unit, ROM, RAM, serial communications ports, ADCs, and so on. In essence, a microcontroller is a computer, but without the monitor, keyboard, and mouse. These devices are called microcontrollers because they are small (micro) and because they control machines, gadgets, and so on.
With one of these devices, you can build an "intelligent" machine. You write a program on a host computer; download the program into the microcontroller via the USB, parallel, or serial port of the PC; and then disconnect the programming cable and let the program run the machine. For example, in the microwave oven, a single microcontroller has all the essential ...