Microcontroller (born Micro Controller Unit, MCU) - chip for controlling electronic devices. A typical microcontroller combines functions on a single chip processor and peripherals, contains RAM and (or) ROM. In fact, this single-chip computer capable of performing simple tasks. 

When designing the microcontroller necessary to balance the size and cost on one hand and flexibility and productivity of the other. For different applications, the optimal ratio of these and other parameters can vary greatly. Therefore, there are many types of microcontrollers with different CPU architecture, size and type of internal memory, a set of peripherals, housing type, etc. Unlike conventional computer microprocessors, microcontrollers often used in Harvard memory architecture, that is, separate storage and commands in the RAM and ROM respectively. 

Furthermore RAM microcontroller may have a built-volatile memory for storing programs and data. Many controllers do not have tires for external memory. The cheapest memory types allow only a single record. Such devices are suitable for mass production in those cases where the controller program will not be updated. Other modifications of the controllers are capable of rewritable nonvolatile memory.