Opening the box

Kelechi repairs laptops from a small table in Computer Village, Ikeja. A customer brings in a laptop that keeps switching itself off, and Kelechi turns it over, undoes ten tiny screws, and lifts off the bottom cover.

The customer leans in, expecting — what? Something complicated. Something mysterious. Instead there is a flat green board with a few black chips on it, a small fan, a strip of copper running from the biggest chip to the fan, two slim cards slotted into the board, and a flat battery taking up half the space. Dust sits in the fan like grey cotton wool.

"That's it?" the customer says. "Where is the computer?"

It is all there. And here is the remarkable thing: after three modules, you could now name every part in that laptop and explain what it does, not from memorising a list, but because you have already built each one, in your head, from switches. This module opens the box. In this lesson you will take a tour of the inside of a real computer and see where everything from Modules 1 to 3 actually lives.

Words in this lesson

A tour of the inside

Here is what Kelechi's customer was looking at, part by part, with where you have already met each one:

In many laptops you will not see a separate GPU, because it is built into the same chip as the CPU. In many thin laptops the RAM is not on removable cards but fixed directly to the board. Different machines arrange things differently, but every computer, from a POS machine to a phone to a server in a data centre, has these same jobs to do.

Notice what is not on the list. There is no part that "thinks", no part that "understands", no part that knows what a file or a photo is. There are switches that calculate, switches that remember, and wires connecting them. You already know that is enough.

The motherboard: roads between the parts

The big green board is the motherboard. Look closely at one and you will see hundreds of fine copper lines printed across it, running from chip to chip like roads on a map. Those lines are wires. Along them travel the bits you met in Module 2 — voltages switching on and off, billions of times a second.

When the processor needs a number from memory, it sends the memory box's address out along one set of wires, and the number comes back along another — exactly as Tiny fetched from box 12 in Lesson 3.5, only with billions of boxes instead of sixteen. A group of wires that carries bits between parts like this is often called a bus — a fitting name, since it carries passengers (bits) between stops (chips) all day long.

Everything plugs into the motherboard or is soldered onto it: the processor, the memory, the storage, the ports on the side of the laptop. Its job is not to compute. Its job is to connect.

Why there are three kinds of memory

You might wonder why a computer needs so many places to keep numbers: registers inside the processor, RAM, and storage. Why not just one?

Think of a busy kitchen at a wedding.

• The cook's hands hold what she is working with this very second — the spoon, the pinch of salt. That is the processor's registers: tiny, but instantly reachable.
• The counter beside her holds everything for the dishes she is preparing now: the chopped onions, the pepper mix, the open bag of rice. That is RAM: much bigger than her hands, quick to reach, but cleared away when the work is done.
• The storeroom at the back holds every ingredient for every event — sacks of rice, cartons of oil. That is storage: enormous, keeps things for months, but a walk away.

No kitchen could work with only a storeroom — imagine walking to the back for every pinch of salt. And no kitchen could fit a storeroom's worth of food on the counter. Computers face exactly the same trade-off. The faster a kind of memory is, the more it costs for each bit and the less of it there is room for. So computers use a ladder: a little very fast memory, more fairly fast memory, and a lot of slower memory, with programs and data moved up the ladder when they are needed.

When you open an app, its instructions are copied from storage (the storeroom) into RAM (the counter), and the processor works on them from there. When you close the app, the counter is cleared. When you save a file, it is carried back to the storeroom. You will look at each step of the ladder closely in the next three lessons.

Heat: why laptops have fans

Every time a transistor switches, a tiny amount of electrical energy turns into heat. One switch makes almost nothing. But a processor has billions of transistors, switching billions of times a second. All those tiny amounts add up to real heat — enough that a processor left with no way to cool would quickly get dangerously hot.

That is what the strip of copper and the fan were for. The copper (part of the heat sink) draws heat out of the chip; the fan blows air across it and out through the vents. Phones have no room for fans, so they spread the heat through their bodies, which is why a phone gets warm during a long video call.

Processors protect themselves. Intel explains that its processors speed up when they have room within their safe temperature and power limits, and that how much they speed up depends on the workload and the heat headroom available — so a hot processor runs slower. This has very practical consequences, especially in a hot country:

• A laptop used on a bed, a pillow or your lap can have its vents blocked. It gets hotter, and slows down to protect itself.
• Dust packed into the fan, like the grey cotton wool in Kelechi's customer's laptop, does the same. That laptop was switching itself off because it was overheating.
• Use a laptop on a hard, flat surface, keep the vents clear, and if it is running hot and loud, have the fan cleaned by someone who knows what they are doing.

Power: the battery and the charger

Nothing in this module works without electricity. The battery stores energy so the laptop can run without a socket. The charger — the box on the cable — changes the electricity from the wall into the steady, low voltage the laptop's parts need.

Two things follow from what you know:

1. When power disappears suddenly, RAM forgets. A laptop's battery protects you from that, which is one reason a laptop with a healthy battery is worth more than one whose battery holds only minutes. You will learn to check a battery's health in Lesson 4.5.
2. Electronics dislike sudden changes in power. When grid power comes back with a jolt, or a generator is switched over, the voltage can spike. Many people plug their computers into a surge protector or a stabiliser for this reason, and unplug them during storms. It costs far less than a new motherboard.

Seeing inside without a screwdriver

You do not need to open your own computer to see its parts — and you should not: opening a laptop can void its warranty, and a damaged battery can be dangerous. Your computer will tell you what is inside it.

On Windows:

• Press Ctrl+Shift+Esc — Microsoft lists this shortcut as the way to open Task Manager. Select the Performance tab. You will see live graphs for the processor (CPU), the memory, each disk, and on many machines the GPU. Open a few programs and watch the graphs move.
• Open Settings → System → About. Under Device specifications, Microsoft says you will find the processor, the amount of RAM installed, and the System type — whether the computer runs 32-bit or 64-bit Windows.

On a Mac:

• Choose Apple menu → About This Mac to see the chip and the memory.
• Open Activity Monitor. Apple's guide explains that it shows how apps are using the processor, memory, disks, network and more.

Every number on these screens now means something physical to you. "CPU 35%" means the processor's switches are busy about a third of the time. "Memory 6.2 GB in use" means about six billion bytes of RAM cells are holding something right now. In the rest of this module, you will learn to read every one of them.

Common mistakes

The short version

• Inside every computer: a processor (CPU) that follows instructions, RAM that holds what is open, storage that keeps everything, a GPU that draws the screen, a motherboard that connects them, and power and cooling.
• The motherboard's copper lines carry bits and addresses between parts.
• Computers use a ladder of memory — registers, RAM, storage — because faster memory costs more per bit. The kitchen: hands, counter, storeroom.
• Billions of switches make real heat. Processors slow down when hot, so keep vents clear and fans clean.
• Task Manager (Ctrl+Shift+Esc), Settings → System → About, About This Mac and Activity Monitor show you what is inside without a screwdriver.

Try it yourself

Take a tour of your own machine.

1. Open Task Manager's Performance tab (Windows) or Activity Monitor (Mac). Write down every part it shows you a graph for.
2. With nothing open, note the CPU and memory numbers. Then open your web browser with five tabs, a document and a music or video app, and note them again. Which part's numbers changed most?
3. From Settings → System → About (or About This Mac), copy down the processor, the installed memory and the system type. Keep this list — you will decode every line of it in this module.
4. Feel where your laptop gets warm, and find its vents. Are any of them blocked by how you normally use it?
5. Explain the kitchen comparison — hands, counter, storeroom — to someone at home, and ask them which part of the kitchen they think a photo they took last year lives in.

You'll know you've got it when you can point to each part of a computer, inside or on a screen, and say what it does, which earlier lesson built it, and why a computer needs more than one kind of memory.