Level 1Unit A · Session 1
1

Unit A · Using a computer

What a computer actually is

What we are making: nothing yet. Today you find out what the machine in front of you is, and get it to do what you tell it.

Photo: the computer lab, machines on, students at them
Photo: the computer lab, machines on, students at them

The idea

A computer looks like one thing. It is really four things joined together, and each one has a different job.

Screen — it showsThis one thinksKeyboard — you typeMouse — you pointOnly one of these four actually does the thinking. The others carry things in and out.
Four parts. Only one of them thinks.

The screen, the keyboard and the mouse are just doors. Things go in through the keyboard and the mouse. Things come out through the screen. The thinking happens in the box, and you never see it.

New words
HardwareThe parts you can touch. Screen, keyboard, mouse, the box.
SoftwareThe instructions. You cannot touch these. Scratch is software.
InputAnything going in. Typing, clicking, a microphone.
OutputAnything coming out. The screen, sound, a printer.
ProgramA set of instructions a computer follows, in order.

Do it — wake it up

  1. Find the power button on the box. It usually has this symbol on it: ⏻
  2. Press it once. Once. Then wait. It takes up to a minute and pressing again makes it slower, not faster.
  3. When the screen asks, type the username and password your teacher gives you.
  4. Wait for the desktop — the screen with the icons on it.
🔧 If it goes wrong
If the screen stays black but the box has a light on, the screen is off or its cable is loose. The computer is fine. Check the screen's own power button first.

Do it — input and output, proved

Three small things, to see the doors working.

  1. Move the mouse. The arrow moves. That is input going in, and output coming back out on the screen.
  2. Open any text program your teacher points you to. Type your name. Same thing, different door.
  3. Now unplug the mouse. Move it. Nothing happens. Plug it back in. Now it works again.

That third one matters. The arrow on the screen is not the mouse. It is the computer's answer to the mouse. Pull the wire and the question never arrives.

⚠ Careful
Never unplug anything without asking. You are allowed to unplug the mouse today because this book told you to, and because a mouse is the one thing that cannot be hurt by it.

Try it — find the four parts

With the person next to you. Point at each one and say what it does. Then answer these without looking back at the diagram.

  1. Which part does the thinking?
  2. The screen is input or output?
  3. Name one input that is not the keyboard or the mouse.
  4. If somebody says 'my computer is the screen', what would you tell them?

If it goes wrong

What you seeWhyWhat to do
Nothing happens when you press powerNot plugged in, or the wall switch is off.Check the wall first, then the back of the box.
It asks for a password you do not haveWrong machine, or it was not set up.Tell your teacher. Do not guess — wrong guesses can lock the account.
The screen is on but everything is hugeSomebody changed the display settings.Tell your teacher. It is a two-click fix but not yours to make.
The mouse arrow jumps aboutDirty sensor, or a bad surface.Wipe the underside. Use a mousemat or a sheet of paper.

What you learned

  • A computer is four parts, and only the box thinks.
  • Input goes in, output comes out. The screen is output.
  • Hardware you can touch. Software you cannot.
  • Press power once, then wait.
Challenge optional — only if you finish early
  • Find out how much memory your computer has, and write it down.
  • Which part of the machine would you replace first if you had the money? Say why.