Fundamentals · Lesson 1

How Computers Work

Every machine in this room is the same machine wearing different clothes

Grades 7 to 12
Time 2 class periods
Difficulty Beginner

There is a 3D printer, a laser cutter, a robot, a tiny board with a screen made of lights, and a computer the size of a credit card in this room. They look nothing alike. Underneath, they are running the same four ideas, and once you can see those four ideas you stop being someone who uses machines and start being someone who understands them. That is the entire difference, and it takes about two periods.

What you'll learn

The four jobs every computer does: input, processing, output, storage
Why everything inside is binary, and what that actually means
How a color, a photo and a sound are all built from numbers, and how to change them
The difference between memory and storage, which almost everyone gets wrong
What a program is and what happens when one runs
How to look at any machine in this lab and name its four jobs

What you need

A computer with a web browser
Your eyes and the room. Day 2 is a walk around the lab.

Day 1

The four jobs

Goal: by the end of today you can explain what a computer is doing, in order, and you know why the answer to "what is it storing" is always numbers.

Step 1: There are only four jobs

Every computer ever built, from the room-sized ones that ran the moon landing to the one in your pocket, does these four things.

Job	What it means	On your laptop
Input	Something comes in	Keyboard, trackpad, camera, microphone
Processing	Something decides what to do	The CPU, doing arithmetic very fast
Output	Something goes out	Screen, speakers, a file, a print job
Storage	Something is kept for later	Your drive, full of everything you have saved

That is the whole shape. Everything else is detail, size and speed.

Why this matters here: the laser cutter is not a mysterious box. It takes a file in, works out a path, and moves a laser along it. Once you can name the four jobs, you can reason about a machine you have never touched.

Step 2: It is all numbers, and there are only two of them

Inside there are no letters, colors or sounds. Just switches, each on (1) or off (0). One switch is a bit. Eight make a byte: 256 patterns, enough for every basic character to get its own number. Agree which number means which letter, and switches can spell.

Checkpoint: you can read off the byte for one letter of your name.

The same trick, everywhere else

Once you accept that a number can mean a letter, the rest follows without any new ideas.

Thing	What the number means
A letter	Its agreed code. `H` is 72.
A color	Three numbers: how much red, green and blue
A photo	Millions of those color triplets, in a grid
A sound	The height of the wave, measured 44,100 times a second
A 3D model	Lists of points in space, and which points connect
A program	Numbers that the CPU reads as instructions

That last row is the strange one and it is worth sitting with. The instructions are stored the same way the photos are. To the machine there is no difference. The difference is entirely in what reads them.

Numbers become color

Your screen is a grid of tiny lights. Each one has a red part, a green part and a blue part, and each part gets one byte: 0 is off and 255 is as bright as it goes. Mix the three like paint made of light.

What you just saw: color

Each light gets one byte: eight switches worth 128, 64, 32, 16, 8, 4, 2 and 1. The number is the switches that are on, added up. All on is 255.
Three bytes is 24 bits, which gives 16,777,216 different colors.
The color codes you see in web design, like #E8421F, are the same three bytes written a shorter way.

Checkpoint: you can make a color with lots of red and no green or blue, and say which switches you turned on.

Numbers become a photo

Zoom into any photo far enough and it breaks into squares. Each square is a pixel, and each pixel is the three color numbers you just played with. Start at 4 by 4, then work up to 96 by 96.

What you just saw: photos

A pixel is three bytes. A phone photo with 12 million pixels is about 36 million bytes before it is squeezed smaller.
More squares means more detail, and more bytes. That is why photos take far more room than text.
A filter is arithmetic. Brighter adds to every number, invert subtracts each one from 255, and no square gets a number below 0 or above 255, because a byte cannot hold one.

Checkpoint: you can find the brightest square in the picture and read out its three numbers.

Numbers become sound

Sound is air pushing and pulling. A microphone measures how hard, thousands of times a second, and every measurement is stored as one number. Play the numbers back in order and you hear the sound again. Two choices decide how good it is: how often you measure, and how precisely.

What you just saw: sound

Measure more often and the shape gets truer. Measure too slowly and it gets misread: at 500 a second, slide the pitch above 250 and you hear a lower note that was never there.
Each number can be rough or precise. 2 bits gives 4 levels and sounds gritty. 16 bits gives 65,536 levels.
CD quality is 44,100 numbers a second at 16 bits, about 88,000 bytes for every second of one channel.

Checkpoint: you can hear the difference between 44,100 and 1,000 measurements a second, and say why the slow one sounds worse.

Step 3: Memory and storage are not the same thing

Nearly everyone mixes these up, including people who have owned computers for thirty years.

Memory (RAM)

Fast, small, and wiped the instant the power goes. It holds what you are working on right now.

This is your desk. Big enough for the things you are actively using, and everything on it hits the floor when you stand up too fast.

Storage (drive)

Slower, much bigger, and it survives being switched off. It holds everything you have saved.

This is the filing cabinet. Slower to get things out of, and still there tomorrow.

This is why unsaved work dies. Your document lives on the desk until you save it. Saving is the act of copying it into the cabinet. The power cut does not delete your work, it just ends the only place your work existed.

Try it: cut the power

Type a few words on the desk. Then try saving, cutting the power, and getting your work back. Predict what will survive before you press anything.

Checkpoint: you can say what survives a power cut, and what you would have to do to keep the rest.

Step 4: Watch a program actually run

A program is a list of instructions. The CPU reads one, does it, moves to the next. It cannot skim.

Checkpoint: you can say why line 3 runs five times, even though the loop only goes round four times.

Fast, and profoundly stupid

On the default setting it takes twenty steps to add up four numbers, and every extra number costs four more. A person does that in their head. The machine needed every single instruction spelled out, in order, with nothing assumed.

Now the other half. Your laptop runs a few billion of those steps every second. It never gets bored, never loses its place, and never decides that is close enough.

This explains two things you already met. Cracking a weak password means trying billions of guesses a second, which is only possible because each guess is a tiny stupid step. And an AI predicting the next word is the same story: a simple operation, run at a scale that stops feeling simple.

Before you leave today

A progress check, not the hand-in. The full submission list is at the end.

Your name converted to bits, screenshotted
You stepped the program to the end and can explain the loop
You made a color from its three numbers and read the numbers of one pixel
You can say the difference between memory and storage without looking

Day 2

Audit the lab

Goal: by the end of today you can walk up to any machine in this room and name its four jobs out loud.

Step 1: Same machine, different clothes

Here are two you already know, filled in for you.

Machine	Input	Processing	Output	Storage
Your phone	Touch, mic, camera	Chip inside	Screen, speaker	Its drive, plus the cloud
MakerBot printer	A sliced file on a USB stick	Board that reads the path	Motors, hot nozzle, an object	The stick, and its own memory

Notice the printer's output is a physical object. That is the only unusual thing about it. Everything else is the same four jobs.

Warm-up: sort the parts

Practice before you walk the room. Pick a machine and tap the job each part does. Some parts do two jobs, and some are hard to place. That is the point.

Step 2: Now you do the rest

Walk the room. For each machine, write the four jobs. Look at the actual thing rather than guessing from memory, and where you are not sure, say so and say why.

The Glowforge laser cutter
A RoboMaster
A micro:bit
A Raspberry Pi
One machine of your choice that is not in this room

Two are deliberately awkward. The micro:bit's storage is tiny and strange, and the RoboMaster's input includes a camera that it uses to make decisions on its own. If a machine does not fit neatly, that is the interesting part. Write down what does not fit.

Checkpoint: five machines, four jobs each, and at least one honest "I am not sure, because".

Step 3: Find the edge

Pick one machine from your list. Everyone writes the base paragraph. High school also writes the stretch, and for middle school it earns bonus points.

Base · everyone

What would happen if this machine lost one of its four jobs? Pick a job, remove it, and describe what the machine becomes.

Stretch · required for HS, bonus for MS

Find something in this room that stores information without being a computer at all. Explain what it stores, how it survives losing power, and why it is not a computer.

Watch: Explained, “Coding”

One episode of the Netflix series Explained, about the history of coding and where it may be going. Underneath it is the idea you have been working with: a machine does exactly what its instructions say, one step at a time.

Watch “Coding” on Netflix (Season 2)
While you watch, listen for someone giving a machine instructions, for one of the four jobs, and for one thing that surprises you.
Then write three sentences for your Watch notes: one thing that surprised you, one thing that connects to the four jobs or to numbers, and one question you still have.

No Netflix at home? Tell Mr. Krigger and you can watch it in class.

Before you leave today

A progress check, not the hand-in. The full submission list is in the Turn in tab.

Five machines audited, four jobs each
You noted at least one thing that did not fit neatly
Your paragraph on the missing job, plus the stretch if you are in high school

What you turn in

Every item comes from an activity you already did. Tick the boxes as you go.

Your name in bits, screenshotted from the converter.
The lab audit: five machines, four jobs each, including one from outside this room.
What did not fit: one part or job that was hard to place, and why, in two sentences.
Your paragraph: remove one job from one machine and say what it becomes. High school adds the stretch.
Watch notes: three sentences on Explained, “Coding”.
Reflection, 3 to 5 sentences: what did you think a computer was before today, and what changed?

Two things to hand in, not one

1 · The assignment

Everything on the previous screen goes here, as file uploads.

Open How Computers Work in Schoology
Click Submit Assignment
Click Upload
Select all your files at once, then Submit

Do not click "Create". Create is for typing text and will not let you attach a screenshot. Upload is the one you want. This is the single most common way work gets lost.

2 · The exit ticket

A separate item in Schoology, taken in class. Short quiz on this lesson, graded on its own.

Either order is fine. Both have to be done.

Name your files so they make sense. lab-audit.pdf tells Mr. Krigger what he is opening. Screenshot 2026-09-14 at 9.03.11 AM.png does not.

Vocabulary

Term	What it means
Bit	One switch, on or off, written as 1 or 0. The smallest thing a computer holds.
Byte	Eight bits together, which is enough for one basic character
Binary	Counting with only two digits, because a switch has only two positions
Pixel	One square of a picture. It is stored as three numbers: red, green and blue.
Sample	One measurement of a sound. A recording is thousands of them every second.
CPU	The part that reads instructions and does them, one at a time, extremely fast
RAM	Working memory. Fast, small, and gone the moment the power is
Storage	The drive. Slower, far bigger, and still there tomorrow
Program	A list of instructions stored as numbers, like everything else
Loop	Instructions that send the CPU back to repeat a section
Input	Anything coming in: a key, a tap, a sensor reading, a file
Output	Anything going out: pixels, sound, a saved file, a printed object

When it goes wrong

The bits converter shows more than 8 digits for one character.

You typed something outside the basic set, like an emoji or an accented letter. Those need more than one byte, which is exactly why they were a mess to get working on the early internet.

I stepped the program and nothing changed.

Some lines only check a condition and decide where to go next, so memory stays the same. That counts as a step. The CPU still had to do it.

Why does it go back to line 3 instead of just repeating?

Because the condition has to be checked every single time. If it did not check, it would loop forever, which is a bug you will write for real at some point.

I cannot work out what the laser cutter stores.

Good, that is the awkward one. Ask what it has to remember while a job is running, and whether it remembers anything after the job finishes. Write down what you conclude and why.

Is a calculator a computer?

Run it through the four jobs and see. It takes input, processes, and outputs. The interesting question is storage, and whether it can follow a list of instructions you wrote. That question is most of what separates a calculator from a computer.