Computers use their CPU (Computer Processing Unit) chip to perform calculations using digital logic circuits, where everything is represented as a 1 or a 0. They work very quickly because the clock speed of the chip is very fast, generally about3 Gigahertz (3 x 10 ⁹ Hertz) these days. This means that the computer completes a step in its calculations 3 billion times per second. A particular calculation may take several steps, but it still won't take very much time!

Modern computer CPU's also make use of multiple processing coressimultaneously so that they can perform multiple tasks at the same timewhich increases the overall speed. This is made possible by making the transistors which make up the digital circuits smaller and smaller so that more of them fit in a small area. The chip size must be kept small or there will be a long delay getting information from one end of the chip to the other since they work so quickly. Current top of the line chips from Intel have over a billion transistors inside them! With this many transistors the chip designers can make more complex circuits which do more complex calculations in short amounts of time.