Punched Cards

by Alicia Tocino

With the help of computers, humans can play music and navigate the Internet. They also help you draw and write, and you can even watch movies with them!

How do they do that? How do computers store all that information?

Computers use binary — that's the language that every CPU or Central Processing Unit understands.

what is the cpu

You now use the keyboard and the mouse to 'talk' to the computer. But, not that long ago, sending instructions to the computer wasn't as easy as it's today.

Instead of a keyboard, humans had to use punched cards to introduce any new program or software. 

Why punched cards, and what do they have to do with binary? Let's find out by playing a game and learn how computers work.


Download and print out one set of 5 punched cards for each human playing the game, as shown in the image below. 

zerus and ona computer basics for kids


Important: Cut out the holes in cards 1, 2, 3, and 4. If you want your cards to look bigger, print this sheet in A3 format.

The numbers 0 through 31 are represented in every card. Each number appears on either one or the other side of the card.


Think of a number between 0 and 31.

zerus and ona computer basics for kids

Take your punched card 0 and search for the number you thought of. Leave the card on the table, looking up. Make sure the chosen number appears on the card's upper side.

zerus and ona computer basics for kids

Now, take your punched card 1 and look for the number you thought of in it. Ensure that the chosen number is on the upper side of it and place it over the card 0, so you don't see the printed side.

Important: You need to be looking at the backside of the card.

zerus and ona computer basics for kids

Go on and do the same with your punched card 2. First, look for the number you thought of, then orient it until the number is placed on the upper side.

Place it over card 1 with its backside facing up.

zerus and ona computer basics for kids

Repeat the same process for your punched cards 3 and 4.

zerus and ona computer basics for kids

zerus and ona computer basics for kids

Do you see a unique number appearing on the upper side?

When you finally place all the cards on top of each other, you'll be able to see only two numbers — an odd number and an even number.

The number that you thought of is on the upper side!

What does all this have to do with computers?

How this game works is similar to how humans sent instructions to the first computers not that long ago.

Humans used punching machines to create punched cards and they had to  place them manually on top of each other when 'writing' programs.

zerus and ona computer basics for kids

Extra Challenge

In this game, you'll find each number from 0 through 31 in every card and because of that, if you'd replace each number for a symbol, the game would still work.

Why don't you replace each number with an emoticon, create your own punched cards for them and replicate the game with your friends?

Important: Remember to always replace each number with the same symbol on every card.


    Curriculum links

    • Mathematics: Number – Exploring numbers in other bases. Representing numbers in base two.
    • Mathematics: Algebra – Continue a sequential pattern, and describe a rule for this pattern. Patterns and relationships in powers of two.



    About the author

    Alicia Tocino is a mathematician and teacher at the University of Malaga in Spain. She has a passion for magic tricks and uses them to turn the classroom into a spectacle for her students.