How Computers Work · Starting Up · Lesson 1 of 5

What Happens When You Press Power

The six steps a computer takes between the button and sign-in.

From button to sign-in

Pressing the power button feels like one moment. Inside, the computer runs a short chain of steps. Each step gets the next one ready. People call this whole process booting, or starting up.

Here is the chain on a Windows 11 PC:

1. Power on. Electricity reaches the main board and the processor wakes up.
2. Firmware. Firmware is a small program stored on a chip on the main board. It is the very first thing that runs. On modern PCs it is called UEFI.
3. POST. The firmware checks that key hardware is present and working. This is the POST, short for power-on self-test. It looks for memory, a keyboard and a drive to start from.
4. Boot loader. The firmware finds the boot loader, a tiny program whose only job is to load the operating system. On Windows it is called Windows Boot Manager. Secure Boot checks it is genuine first.
5. Operating system. The boot loader loads Windows into memory and hands over control.
6. Drivers and sign-in. Windows starts its helpers, then shows the sign-in screen.

If something fails early, you often see a clue. A PC that beeps or shows a logo and stops may have a hardware problem caught by the POST. A message like "no bootable device" means the firmware could not find a boot loader.

Phones work the same way. They also run firmware first, then check and load their system.

On the practice computer, press power and step through each stage. Tap a stage to read what it does.

Drivers, services and a fresh start

Once the boot loader hands over, Windows still has work to do before you see your desktop.

First it loads drivers. A driver is a small program that lets Windows talk to one piece of hardware. Your screen, Wi-Fi, sound and printer each need one. Without the right driver, the part may not work at all.

Next it starts services. A service is a program that runs quietly in the background. One handles updates. Another handles the network. Another runs Windows Security. You never see most of them.

Then the sign-in screen appears. After you sign in, your startup apps open. These are apps set to start every time, like a cloud storage app.

This order explains a lot of everyday problems:

• A bad driver, often after an update, can stop Windows partway through starting.
• Lots of startup apps make the time after sign-in feel slow.
• A frozen service can make the computer act strangely until it restarts.

One more detail. Windows 11 has a feature called Fast startup. When you choose Shut down, Windows saves part of its running state so the next start is quicker. Restart does not do this. It runs the whole chain from the very beginning.

That is why Restart is the better choice when something is acting up. It gives drivers and services a truly fresh start. It also finishes installing many updates.

On a Mac, the steps are similar. The Mac checks its own startup software before macOS loads.