How does a computer keep a picture? Inside a computer, things such as pictures are stored with only 0s and 1s. A bit is the smallest piece of computer storage, and it holds a 0 or a 1. Binary is a number system that uses only two digits.

A byte is a group of 8 bits. One byte can store one letter or other character, such as A. Each extra bit doubles the number of different patterns that bits can make. A byte, which is 8 bits, can make 256 different patterns.

A picture on a computer screen is made of many tiny squares called pixels. A picture is stored as a long list of numbers. Computers can also squeeze pictures and sound into less space. This is called compression.

A program is a list of instructions for a computer. Before a program runs, the computer copies it from storage into RAM. RAM is fast memory that holds the programs and files a computer is using right now. When the power is turned off, RAM loses what it holds. This is only a simple picture, because a real computer has many more parts and steps.

Where do the bits live? A bit is stored as electric charge in a chip, but as magnetism on a hard disk. Files that are saved on a computer's drive are still there when the power goes off. So the bits that make a picture can stay safe on a drive until the computer needs them.

Words to know

• compression: squeezing data
• binary: two-digit system
• pixels: tiny squares
• RAM: fast memory