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Definition: microcontroller

A single chip that provides computer processing in everything from toys to appliances to automobiles. A microcontroller unit (MCU) contains the processor (CPU), non-volatile memory for the program (flash memory or ROM), volatile memory for processing the data (RAM), a clock that makes everything go and an I/O control unit that handles input to and output from the chip. Every year, billions of microcontrollers are manufactured.

Microcontroller units (MCUs) are available in numerous sizes and architectures. The MCU was actually the first "system-on-chip" (SoC) but that term was coined later for large chips with several sophisticated components (see SoC). See CPU, flash memory, ROM, RAM and clock.

They Don't Get the Publicity
Because MCUs contain only 8-, 16- or 32-bit CPUs and cost just a few dollars or even less than one dollar, they never get the mainstream attention like the latest Intel CPUs that can retail for several hundred dollars. In addition, MCUs are not the kind of chip that users buy to replace an old and slower CPU in their PCs. MCUs are built into products at the time of manufacture. They also do not require state-of-the-art semiconductor technology as do the latest chips in phones, laptops and desktop computers (see process technology). See embedded system and automotive systems.

Motorola 6801 - One of the First
Introduced in 1978, the 6801 was one of the first MCUs to claim the "computer on a chip" moniker. These magnified images show the entire chip (top), most of the 256 bytes of RAM (left) and only two bytes at 400x (right). At 400x magnification, a single byte in today's state-of-the-art chips would not be observable at all.

They Don't Get Much Smaller
These 8-bit microcontrollers (PIC brand) from Microchip in Tempe, Arizona are used in myriad applications, cost less than 50 cents in quantity and are a lot more powerful than the Motorola 6801 in the above image. We're not great at predicting technology. In 1949, Popular Mechanics speculated that future computers would only weigh "one and a half tons!"

A Microcontroller Behind Everything
Today's vehicles can have a hundred or more MCUs, each controlling the simplest function from pressing a button to more complicated systems like the ones in the Honda above.