By the end of this lesson you will be able to
- Describe in order what happens between pressing the power button and seeing the desktop.
- Explain what firmware, a bootloader and an operating system each do at start-up.
- Explain why starting a computer takes time and why it needs to read from storage.
- Use the words boot, log in, desktop, icon, window, cursor, app and file correctly.
When you press the power button, a lot happens in the few seconds before you can use your computer. Knowing the order helps you in two ways: you understand why a laptop sometimes takes a while to be ready, and you can tell roughly where things have gone wrong when it does not start. At the end you will also have the everyday words you need for the rest of the academy.
Why a computer cannot just switch on
Your programs and documents are kept in storage, which keeps its contents when the power is off. But the processor can only work on instructions held in memory (RAM), and RAM forgets everything when the power goes off. So every time you switch on, the computer must copy the operating system from storage into memory. Starting up like this is called booting, from an old saying about pulling yourself up by your own bootstraps.
There is a puzzle here. The processor needs instructions to load the operating system, but the operating system is the thing that holds the instructions. The answer is a small program that is built into the computer's circuit board and never disappears. We call this built-in program Firmware.
From power button to desktop
- Step 1: Power buttonElectricity reaches the parts
- Step 2: Firmware startsUEFI runs a quick self-test
- Step 3: Bootloader foundFirmware looks on the drive
- Step 4: System loadsOperating system is copied into RAM
- Step 5: Login screenDrivers and services are ready
- Step 6: DesktopYou can start using the computer
Read this figure as text
A flow of six steps from the power button to the desktop.
Step 1: you press the power button and electricity flows to the parts. Step 2: the firmware (UEFI) starts and does a quick power-on self-test to check that the memory, processor and other basics respond. Step 3: the firmware finds the bootloader on the storage drive. Step 4: the bootloader loads the operating system into memory. Step 5: the operating system starts services and drivers and shows the login screen. Step 6: you log in and the desktop appears.
Stage 1: firmware and the self-test
On modern computers the firmware is called UEFI. Older machines used a similar program called BIOS, and many people still say BIOS for both. As soon as power arrives, UEFI wakes the basic hardware and runs the power-on self-test. It is a quick check that the processor, memory and other essentials respond. If something important is missing, a desktop may beep or flash lights instead of showing a picture.
Stage 2: the bootloader
Next, UEFI looks at the storage drive for a small program called a Bootloader. Its only job is to find the operating system and start loading it. On Ubuntu the bootloader is usually GRUB; on Windows it is the Windows Boot Manager. If you have both installed, the bootloader may offer you a menu to choose between them.
Stage 3: the operating system loads
The operating system (Ubuntu or Windows) now copies the parts it needs into memory. It starts the kernel, its core, and loads drivers: small programs that let it talk to the screen, keyboard, Wi-Fi and other hardware. It also starts background services, such as the one that connects to your Wi-Fi network. Many of these take a moment, which is the main reason starting takes time. Reading many files from storage and preparing everything is slower than people expect.
Read this figure as text
A sequence diagram of the power button, firmware, bootloader and operating system passing control along.
Four actors in order: the power button, the firmware, the bootloader and the operating system. The power button sends power to the firmware. The firmware checks the hardware and then hands control to the bootloader. The bootloader finds the operating system on the drive and loads it into memory. The operating system then takes over and shows the login screen. Each actor does a small job and passes control along, like a relay race.
The login screen and the desktop
When the system is ready, you see the login screen. To log in means to tell the computer who you are, usually by choosing your name and entering your password, so it can open your own files and settings. Your account keeps your things separate from anyone else who uses the computer. Never share your password and never write it on a sticker on the laptop.
After you log in, the desktop appears. This is the main screen you work from. Ubuntu and Windows look different but have the same ideas, as the two simulated desktops below show.
- Marker 1: Activities: search and switch
- Marker 2: Clock and notifications
- Marker 3: System menu: sound, Wi-Fi, power
- Marker 4: Dock: favourite and running apps
- Marker 5: A window containing an app
Read this figure as text
A simulated Ubuntu desktop with the Activities button, clock, system menu and dock labelled.
A simulated Ubuntu desktop. The Activities button at the top left opens the overview where you can search and switch windows. The clock at the top centre shows the time and, when clicked, the calendar and notifications. The system menu at the top right holds volume, network and power settings. The dock down the left side holds favourite apps and shows which apps are running. An open window sits in the middle. Real Ubuntu releases may differ slightly.
- Marker 1: Start button and menu
- Marker 2: Search for apps and files
- Marker 3: Taskbar: pinned and running apps
- Marker 4: Status icons: Wi-Fi, sound
- Marker 5: Clock and date
- Marker 6: A window containing an app
Read this figure as text
A simulated Windows desktop with the Start button, search, taskbar, tray and clock labelled.
A simulated Windows 11 desktop. The Start button on the taskbar opens the Start menu with your apps and the power options. The search box finds apps and files. The taskbar along the bottom shows pinned and running apps. The system tray at the right holds small status icons such as Wi-Fi and volume, and the clock sits at the far right. An open window sits in the middle. Real Windows builds may differ slightly.
Everyday words you now need
| Word | What it means | Example |
|---|---|---|
| Boot | Starting the computer and loading the operating system. | “The laptop takes a minute to boot.” |
| Log in | Telling the computer who you are so it opens your account. | Choose your name and enter your password. |
| App | A program you use to do a job. Short for application. | A web browser, a music player. |
| File | One named piece of saved information. | A letter saved as letter.odt. |
| Icon | A small picture that stands for an app, file or folder. | The picture of a folder. |
| Window | A rectangle on screen that holds one app or one folder. | A browser window. |
| Cursor | The arrow or mark that shows where you point; the text cursor is the blinking line in text. | Move the mouse and the arrow moves. |
Switching off, restarting and sleeping
Shut down closes everything and switches the power off. Restart shuts down and immediately boots again, and is the standard fix for many small problems and for finishing updates. Sleep keeps your work in memory and uses a trickle of power, so waking takes seconds and nothing needs to boot. Hibernate saves memory to storage and switches off, so it uses no power but takes a little longer to wake. Always shut down properly instead of holding the power button, because the computer needs a moment to close files safely.
- Do lights or fans react when you press the power button?
- YesDoes anything appear on the screen?
- YesDoes the logo or login screen appear?
- YesDo thisThe start-up stages worked. Any problem is now in the desktop or in a program.
- NoDo thisThe firmware cannot find the system on the drive. Do not reinstall anything yourself yet. Note the exact message and ask a technician or use recovery help.
- NoDo thisTurn up the brightness, wait a minute, and try an external monitor if you have one. Then ask for help.
- YesDoes the logo or login screen appear?
- NoDo thisCheck the charger, the socket and that the battery is not flat. Leave it charging for 30 minutes and try again.
- YesDoes anything appear on the screen?
Read this figure as text
A decision tree that uses what you see on screen at start-up to guess the stage that failed.
Start: does anything light up or make a sound when you press the power button? If no, check the charger, the socket and the battery; this is a power problem. If yes: does anything appear on the screen? If no, the screen may be dark or the brightness low; try an external screen or wait a minute. If yes: does a logo or login screen appear? If no, and a message such as no operating system found or no bootable device appears, the firmware cannot find the system on the drive, so the drive or start-up settings need a technician or a recovery step. If yes, the system has started, and any problem is later, in the desktop or a program.
Common mistakes
✖ Instead of: Pressing the power button again and again when the screen is slow to appear.
✔ Do this: Wait a minute. Booting takes time. Repeated presses can interrupt start-up or switch it off.
✖ Instead of: Thinking the login password and the Wi-Fi password are the same thing.
✔ Do this: The login password opens your account on this computer. The Wi-Fi password lets the computer join a network. They are separate.
✖ Instead of: Changing settings in the UEFI screen out of curiosity.
✔ Do this: A wrong change can stop the computer starting. Look if you want to, but leave it unchanged and exit without saving.
If something goes wrong
- The laptop does nothing when I press the power button.
- Plug in the charger, check the socket works, and leave it for about 30 minutes in case the battery is flat. Then try the button again.
- The screen stays black but I can hear the fans.
- Turn up the brightness keys, wait a minute for a slow start, then check with an external monitor if you have one. If it still stays black, ask a technician.
- A message says “No bootable device” or “Operating system not found”.
- Remove any USB drive or memory card that is plugged in and restart, because the computer may be trying to start from it. If the message returns, note it exactly and get help.
Key terms
- Boot
- The process a computer goes through when it is switched on, ending with the operating system running.
- Firmware
- Small built-in software stored on a hardware device that starts and controls it.
- UEFI
- The modern kind of firmware on a computer's motherboard that starts the hardware and then hands over to the operating system.
- Bootloader
- A small program that finds the operating system on the drive and starts loading it.
- Power-on self-test (POST)
- A quick check the firmware runs at start-up to see that the memory, processor and other basics respond.
- Login
- Proving who you are, usually with a password, to start using a computer or account.
Practise it for real
Reading is not the same as being able to do it. Complete these on your own computer, then tick only what you have actually done. These ticks are your own honest record: nothing checks them for you.
Watch a start-up and name each stage
Shut down your laptop from the system menu (Ubuntu) or the Start menu (Windows). Wait for the lights to go off, then press the power button. Watch the screen and time it with a clock or phone. Note when you first see a logo (firmware and bootloader), when you see the login screen, and when the desktop appears. Log in as you normally do. This is your own computer and the usual sign-in, so nothing special is needed. Then write down the three times.
Challenge: name the parts of your own desktop
With your desktop showing, point to and say the name of: one icon, one window you have opened, the cursor, the clock and the place where running apps are shown (dock or taskbar). Open one app, then close it. Then explain to someone, without notes, the difference between a file and an app.
Knowledge check
7 questions. You need 80% to pass. Mistakes here are part of learning, and you can retry as often as you like.
Summary
- RAM forgets when the power is off, so the operating system is loaded from storage at every start.
- Order: power, firmware and self-test, bootloader, operating system, login screen, desktop.
- Logging in tells the computer which account to open. Never share the password.
- Shut down from the menu; avoid holding the power button unless the computer is frozen.
- Boot, log in, app, file, icon, window and cursor are the core words for everything that follows.
Checklist: can you do these?
Marking a lesson as read does not prove you can do it. Skills count as demonstrated when you pass the quiz (not yet) and complete the practical tasks (not yet).
Related lessons
References and further reading
Official sources for details that can change between versions.
- Ubuntu documentation (Ubuntu)
- Windows 11 support: start-up and shutdown (Microsoft)