What is a computer network

Reaching a Friend Far Away

With just one computer, you can write and draw on your own. But if you want to send what you wrote to a friend who lives far away, things are different.
There has to be a path between the two computers for anything to travel along. Without one, however good your writing is, it stays inside your own computer.
The moment a path appears, you can finally say something to your faraway friend.

Tap the left computer and then the right one to link them. Once the path is there, press send and a short hello crosses over.

Once the two computers were linked, the words crossed over despite the distance. Linking computers so that they can talk to each other like this is the first step of a network.
So what is that path actually made of?

What Do We Link Them With?

There are two main kinds of path between computers. One is a wire, a visible cable that joins two computers directly. The other is wireless, which sends signals through the air with no cable at all.
The Wi-Fi you use at home or in a café is the best-known example of wireless.
The methods differ, but the job is the same: opening a path between two computers.

Press the wire and wireless buttons in turn and the way the two computers are linked changes. They look different, but both are paths that link computers.

Wire or wireless, the job was exactly the same: opening a path for signals to travel between two computers. You can hold a wire in your hand, while wireless is simply invisible.
So what travels along that path?

What Travels the Path Is 0s and 1s

The letters and pictures I send change form while they cross the path. We learned earlier that everything inside a computer comes down to 0s and 1s.
Messages are no different. The letters turn into a row of 0s and 1s, and that row becomes a signal that crosses the path.
The computer on the other side turns the row it receives back into letters and reads them.

Press send and the letter A turns into a signal made of a row of 0s and 1s, crosses over, and becomes the letter A again on the other side.

The letter turned into 0s and 1s and then back into a letter. What travels along the path is always this one kind of signal.
Photos, voices, videos: look inside and they are all 0s and 1s. That is why a single path can carry every kind of thing.

When Many Are Woven Together Like a Net

If only two computers are linked, only those two can talk. But there are countless computers in the world.
What happens if you link three, four, or a great many computers to one another? Wires and signals weave together like a net, and from any computer you start at, you can reach the computer you want.

Tap the dashed lines between the five computers, A to E, one by one to link them. Once the net is complete, even two computers with no direct line reach each other through others.

With the net complete, computers far apart reached each other by way of other computers. Even without being right next to each other, the signal crossed over by passing through computers in between.
This enormous net of countless computers woven together across the whole world is what we call the internet.

Summing Up

In one line: a network is computers far apart talking by trading signals.
The path is made by wire or wireless, and what travels along it is, in the end, 0s and 1s. When many computers are woven together like a net, you can reach anyone, and that enormous net is the internet.

Tap the four key points in order to review them. (link far apart → wire or wireless → 0 and 1 signals → woven like a net = internet) When all four are lit, the review is done.

Now you know what a network is: linking faraway computers by signal, like a net.
But how do we send large data, like a photo or a video? The path is too narrow to send it all in one piece.
The next lesson is about packets, which split large data into small pieces before sending it.