People use all kinds of symbols, sounds, colors and body motions to express themselves. These expressions are, in a sense, codesâ€”signals we use to communicate with one another.

Computers use a special code of their own to express the digital information they process. It's called the binary code because it consists of only two symbolsâ€”0s and 1s. (The "bi" in "binary" means two.)

Why 0s and 1s? Because those are the only two numbers you need to express the flow of electricity through a transistor. It's either on or it's off. On is 1, off is 0. Everything you say to a computer has to be put in terms of these two numbers.

Lesson 1: What is Binary Code?