Your games, your website, your photos: the computer stores every one of them as 0s and 1s. Today you will encode a short message by hand, colour a tiny picture from a bit pattern, then decode someone else's bits back into letters and a drawing. By the end you will be able to explain how numbers, text and images all become binary.
Quick hook: hold up a phone photo or point at a game on the board and ask how does the computer actually store this? Take one or two guesses, then move on. No devices needed today: this is paper, pencils and a grid. Have scrap paper and a few spare pencils ready.
A bit is the smallest piece of data a computer can store. It is either a 0 or a 1. Everything a computer keeps is built from bits.
Numbers. Binary counts in powers of two. With four bits you can store the numbers 0 to 15 (for example 0001 = 1, 0101 = 5, 1111 = 15).
Text. Every letter is first given a number, then that number is stored as bits. Today you will use this short class code (not the full computer code, just enough to send a message):
- A = 0001
- B = 0010
- C = 0011
- D = 0100
- E = 0101
- H = 1000
- I = 1001
- L = 1100
- O = 1111
- space = 0000
Keep this tight: the making is the learning. Write the class code table on the board and leave it up for the whole lesson. Common misconception: students think computers "see" letters the way we do. Push the chain: letter → number → bits. Model one letter live on the board as the full chain, for example H → 8 → 1000, and point at each stage as you write it.
Do not introduce ASCII or file sizes unless a strong student asks; stick to the class code. Pixels come in the next content beat after they have practised text.
Work on paper. Keep the class code table where you can see it.
- Encode a short message. Choose a word or short phrase using only the letters in the class code (A, B, C, D, E, H, I, L, O and space). Good options: HI, HELLO, CODE, BAD, CAB.
- Write each letter, then write its 4-bit code underneath. Leave a gap between each group of four bits so it stays readable.
- Example: HI becomes 1000 1001.
Done looks like: your message written as letters and as groups of four bits.
Circulate and check groups of four bits stay grouped; students often run bits into one long string and then cannot decode. If someone finishes early, challenge them to encode a two-word phrase with a space (0000) between the words.
Look-fors:
- bits written in clear groups of four
- each group matches the class code table
Images. A picture on a screen is a grid of tiny dots called pixels. In a simple black-and-white image, each pixel is one bit: 1 means colour it in, 0 means leave it blank. Line the bits up in rows and a picture appears.
Sketch a 4×4 grid live and colour two cells so they see a pixel light up from a 1. Point at the diagram: each cell is one pixel and one bit. Do not introduce RGB unless a strong student asks; stick to 1-bit pixels today.
Stay on paper.
- Colour a pixel grid from bits. Draw a 4 by 4 grid (16 squares). Use this bit pattern, reading left to right across each row, top row first:
Row 1: 0 1 1 0
Row 2: 1 1 1 1
Row 3: 1 0 0 1
Row 4: 0 1 1 0
Colour a square when the bit is 1. Leave it blank when the bit is 0. What picture did the bits make? Name it in a few words (for example smile, window, letter O). Any reasonable answer is fine. - Make your own 4 by 4. Design a tiny black-and-white picture (a letter, a simple face, a cross, an arrow). Write the 16 bits that store it, row by row. Keep this pattern: you will swap it with a classmate later.
Done looks like:
- the given bit pattern coloured in on a 4 by 4 grid
- your own 4 by 4 picture with its 16 bits written underneath
Suggested timing: about 4 minutes on the given grid, 5 on their own design.
If someone finishes early, offer an 8 by 8 grid for a clearer picture. Look-fors: grid coloured from the pattern, not freehand; their own design's bits match the squares they coloured.
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