When teaching computing this is a really good place to start. At first, computers seem to be able to analyse incredibly complex information. But in fact they actually process an enormous amount of simple information very quickly.

Inside a computer are electrical wires and circuits that carry all of the information in a computer. In a single wire with electricity running through it the signal can be either on or off. This can be represented as a 1 (on) or 0 (off). This on / off state of a single wire is called a ‘bit’ and is the smallest piece of information that a computer can store. If you use more wires you get more bits, more ones and zeros. With more bits you can represent more complex information.

To understand this complex information we need to understand something called the ‘Binary Number System’.

We learned to count with the decimal number system with digits from 0 to 9. With the binary number system we only have two digits, 0 and 1.

With the decimal system the place value of numbers goes up by factors of 10 (1,10,100,1000). With the binary system, the place value goes up by factors of 2 (1,2,4,8,16). Here is the number 9 represented by the decimal system (also known as base-10 system) and the binary system (base-2).


1000 100 10 1


8 4 2 1
1 0 0 1
(1×8) +  (0x4) +  (0x2)  +  (1×1) = 9

Any number can be represented this way. Information that is stored in a computer as text, images or sound can also be represented with numbers. With letters for example, each letter can be assigned a number. You can then represent any word or paragraph as a sequence of numbers. These numbers can be stored as on or off electrical signals.


4 15 7
0 0 1 0 0 0 1 1 1 1 0 0 1 1 1

All photos, videos and images you see on screen are made out of tiny dots called pixels. Each pixel has a colour and each colour can be represented by numbers.

Every sound is basically a series of vibrations in the air. Vibrations can be represented graphically as a waveform. Any point on a waveform can be represented as a number. In this way, any sound can be broken down into a series of numbers.

To introduce children to the binary number system unplugged computing ideal as it makes something that at first seems quite abstract into something much more concrete. There are many fantastic unplugged activities available online. Here is one to get you started.

How binary digits work

Prepare Binary cards (found here)

  1. Hold the first 5 cards (1, 2, 4, 8 and 16 dots), but don’t let students see the dots. Ask for 5 students to volunteer to be “bits”, and have them stand in a line in front of the class.
  2. Hand out the 1-dot card to the person on the right. Explain that they are one “bit” (binary digit), and can be on or off, black or white, 0 or 1 dot. The only rule is that their card is either completely visible, or not visible (i.e. flipped over). Hand out the second card to the second person from the right. Point out that this card has either 2 dots (visible), or none (upside down).
  3. Ask the class what the number of dots on the next card will be. Get them to explain why they think that.
  4. Silently give out the four-dot card, and let them try to see the pattern.
  5. Ask what the next card is, and why.
  6. Students should be able to work out the fifth card (16 dots) without help.
  7. Remind the students that the rule is that a card either has the dots fully visible, or none of them are visible. If we can turn cards on and off by showing the front and back of the card, how would we show exactly 9 dots? Begin by asking if they want the 16 card (they should observe that it has too many dots), then the 8 card (they will likely reason that without it there aren’t enough dots left), then 4, 2 and 1. Without being given any rules other than each card being visible or not, students will usually come up with the following representation.
  0            1          0           0           1        =     9
  1. Now show how different numbers can be made using different combinations of cards. Start with the smallest number possible then work up. Then give the children the opportunity to make their own numbers using small binary number cards or whiteboards. This activity can be differentiated by groupings / number of cards given.
  2. Discuss patterns that the children may come across e.g. When is the 1 card ‘on’? What is the largest number I could make? What would happen if I needed to make a larger number? Add another card. How many dots would this card have?

Discuss different ways in which ‘on’ and ‘off’ could be represented (e.g. Holding the cards high and low, standing up or sitting down etc). Think how else two contrasting values could be represented in writing or graphically (tick and cross, happy and sad face etc).

Once children understand how the binary number system works they can then use it display a variety of information, from text to images, all using unplugged activities!


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