# Unit plan: Binary numbers

Computers today use digits to represent information - that's why they're called digital systems. The simplest and most common way to represent digits is the binary number system, with just two digits (usually written as 0 and 1). It is called binary because there are only two different digits used, or two states.

See teaching this in action

A bit is usually stored in a memory cell inside a computer, which is an electronic circuit that can be set to a high voltage level (1) or a low voltage level (0); on disks they are represented by magnetism or optical reflection.

There are billions of these bits on a typical computer, and they are used to store text, numbers, images, video, and anything else that we need to store or transmit. On computer networks the bits are communicated by light, voltages or sound. Anything that can have two different values …

## Lessons

Ages 5 to 7 Programming challenges
In the teacher observations sections there may also be background notes on the big picture. There is no expectation that 5 to 7 year olds will need to know this, but if you are asked, you have the answer at your fingertips.
1 How binary digits work No
2 Reinforcing sequencing in binary number systems No
3 Codes for letters using binary representation No
Ages 8 to 10 Programming challenges
1 How binary digits work Yes
2 Reinforcing sequencing in binary number systems No
3 Codes for letters using binary representation No