Central Processing Unit (CPU)

The CPU is the brain of a computer, containing all the circuitry needed to process input, store data, and output results.

The CPU is constantly following instructions of computer programs that tell it which data to process and how to process it. Without a CPU, we could not run programs on a computer.

For example, a simple calculator program might instruct the CPU to take two numbers, 2 and 2, add them, and send back the result.

An illustration of a CPU. The CPU is shown as a tall rectangle with silver pins coming out of the left and right sides. An arrow flows from the left with binary numbers and arrow flows to the right with more binary.

The CPU can process those instructions easily, thanks to a control unit that knows how to interpret program instructions and an Arithmetic Logic Unit (ALU) that knows how to add numbers. With the control unit and ALU combined, the CPU can process much more complex programs than a simple calculator.

Inside the CPU

At the hardware level, a CPU is an integrated circuit, also known as a chip. An integrated circuit "integrates" millions or billions of tiny electrical parts, arranging them into circuits and fitting them all into a compact box.

Photo of an Intel chip, covered in gold and wires.

An Intel 80486DX2 CPU chip. Source: Matt Gibbs, Wikipedia Commons

We can visualize the layers of the CPU chip:

Four labeled illustrations of computer parts, stacked from top to bottom. At the top is a chip, then a logic circuit, then a logic gate, and then a transistor and wire.

Some of those layers are physical devices, like the chip and transistors, and some of those layers are abstractions, like logic circuits and gates.

It's impressive that we can put together seemingly simple devices like logic gates to create CPUs that power complex devices like our phones, computers, and even self-driving cars.