What a computer actually is

It is Monday morning at a POS stand in Yaba. A man hands Mama Tobi his card. She presses a few buttons, the little machine thinks for two seconds, prints a slip, and ₦20,000 leaves his bank and lands in his brother's account in Kano before he has put his wallet back in his pocket.

Ask Mama Tobi what just happened and she will say, "The machine did it." Ask her what the machine is and she will laugh: "It's a POS."

It is also a computer. So is the phone in her pocket, the ATM down the road, and the prepaid meter that decides whether her shop has light. By the end of this course you will know what happened inside that POS machine — not roughly, but properly, all the way down to the sand it was made from. This lesson starts with the simplest question, the one most people never actually answer: what is a computer?

Words in this lesson

A computer is a machine that follows instructions

Here is the whole idea in one sentence: a computer is a machine that takes in information, follows instructions to change it, and gives a result back.

Notice what that sentence does not say. It does not say a computer is clever. It does not say it thinks, wants, or decides. A computer does exactly what its instructions say — nothing more, nothing less — and it does it extremely fast.

Think of a very obedient cook who cannot read your mind. If the recipe says "add one cup of salt", this cook adds one cup of salt, even though you meant one teaspoon. The cook is not stupid and not wicked. The cook simply follows the recipe. A computer is that cook, except it can follow billions of steps every second without ever getting tired.

Everything a computer seems to "know" was put there by people: the instructions, the information, the rules. That is good news for you. It means nothing about a computer is magic. Every part of it can be understood, and by the end of this course, you will understand it.

Four jobs every computer does

Every computer, from the biggest in a bank's data centre to the smallest in a pocket radio, does the same four jobs.

1. Input — information goes in. You press a key, tap the screen, speak into the microphone, point the camera at something, or slide a card into a machine.

2. Processing — the computer works on it. It follows instructions to change that information: add numbers, compare them, rearrange them, decide which step comes next.

3. Output — a result comes out. Something appears on the screen, a sound plays, a slip prints, money moves, a light turns on.

4. Storage — it keeps things for later. Your photos, your contacts, your messages, the bank's record of what you paid. Storage is why your phone still has your WhatsApp chats when you switch it back on tomorrow.

A worked example: taking a photo

Follow one photo through your phone:

• Input: light from the scene enters the camera and is turned into information.
• Processing: the phone follows instructions to sharpen the picture, adjust the colours and decide how bright it should be.
• Output: the finished picture appears on your screen.
• Storage: the photo is saved, so it is still in your gallery next week.

A second worked example: Mama Tobi's POS

• Input: the card's details, the amount typed in, the account number.
• Processing: the machine follows instructions to package the request and send it to the bank, then checks the reply.
• Output: the screen says "Approved" and the slip prints.
• Storage: a record of the payment is kept — on the machine and at the bank.

Once you see these four jobs, you will see them everywhere.

Computers you walk past every day

Most of the computers in your life do not look like computers. They are hidden inside other things:

• Your phone — a powerful computer that also makes calls.
• A POS machine — a small computer built to take payments.
• An ATM — a computer with a cash box attached.
• A prepaid electricity meter — a computer that counts the units you use and switches your supply off when they run out.
• A car — modern cars contain many small computers controlling the engine, the brakes and the dashboard.
• A microwave, a smart TV, a decoder — each has a computer inside following instructions.

None of these have a keyboard and a big screen, yet each takes in information, follows instructions, gives a result and keeps something for later. That is what makes them computers. A laptop is not "more of a computer" than a POS machine. It is simply a computer built to do many different jobs instead of one.

The one thing a computer cannot do: decide for itself

Because a computer only follows instructions, it will happily follow wrong ones.

Imagine Mama Tobi types the account number and gets one digit wrong. The machine does not stop and say, "This looks like a mistake, I think you meant the other one." It sends the money to the account she typed. People sometimes call this "garbage in, garbage out": wrong information going in produces wrong results coming out, however perfect the machine.

This is also why computers can feel stubborn. When a website refuses your password because one letter is a capital, the computer is not being difficult. It is comparing exactly what you typed with exactly what it stored, and they are not the same.

Understanding this changes how you use computers. Instead of thinking "the computer is against me", you start asking "what exactly did I give it, and what exactly was it told to do?" That question solves most computer problems — you will use it in every module of this course.

Hardware and software: the body and the instructions

A computer has two halves that need each other.

Hardware is everything you can touch: the screen, the keyboard, the battery, and the chip inside that does the processing. Hardware on its own does nothing — like a brand-new kitchen with no recipe and no cook.

Software is the instructions: the apps, the programs, the system that starts when you switch on. Software cannot exist without hardware to run on, and hardware is useless without software to follow.

When your phone updates overnight and suddenly has new features, the hardware did not change at all. Only the instructions did. That is the power of software, and you will learn exactly how it works in Module 5.

Where this course is going: from sand to a talking rock

Here is something true and strange. The chip that did the processing in Mama Tobi's POS machine is made mostly of silicon — and silicon is made from sand. People took sand, purified it, printed billions of tiny switches onto it, and taught those switches to count, to remember, to send messages across the ocean and, lately, to answer back in words. A rock that talks.

This course follows that journey in order:

1. From sand to switch — what a computer is made of (this module).
2. Counting with switches — how on-and-off becomes numbers, letters, pictures and sound.
3. Teaching switches to think — how switches make decisions and remember.
4. Inside the machine — the processor, memory and storage, and how to choose a laptop.
5. Software — how instructions tell the rock what to do.
6. Files — where your work actually lives.
7. The internet — how a message crosses the ocean.
8. Working online — email, the cloud, documents.
9. Staying safe — how attackers think, and how to beat them.
10. The talking rock — how artificial intelligence works.
11. Own it — putting everything together.

You do not need to remember that list. You only need to trust that every lesson stands on the one before, so nothing will be thrown at you without the ground under it.

Common mistakes

The short version

• A computer takes in information, follows instructions to change it, gives a result, and keeps information for later.
• Every computer does four jobs: input, processing, output and storage.
• Computers are hidden in phones, POS machines, ATMs, meters, cars and more.
• A computer does exactly what it is told, so wrong input gives wrong output.
• Hardware is what you can touch; software is the instructions it follows.
• This course explains the whole machine, starting from the sand it is made from.

Try it yourself

The computer hunt. Take a page in a notebook, or a new note on your phone.

1. List every computer you used, touched or depended on since you woke up today. Aim for at least ten. Remember the hidden ones: the meter, the POS, the bus that takes card payments, the bank app.
2. Pick five of them. For each one, write its input, its processing, its output and its storage, in one line each.
3. Find one moment from your own life when a computer "got it wrong". Write down what the input was, and whether the machine actually made a mistake or did exactly what it was told.
4. Explain to someone at home, in three sentences and without the word "magic", what a computer is.

You'll know you've got it when you can look at any machine around you — a lift, a fuel pump, a set-top box — and say out loud what its input, processing, output and storage are, and when "the computer made a mistake" makes you ask what it was given instead.