Why does turning it off and on again actually work?

Liz's meeting starts in two minutes. Her laptop picks this moment to freeze. Even the mouse pointer won't move.

“Restart it,” says Dan.

“Why does that always work?” says Liz. It's a fair question. It's the oldest advice in tech support, and it works so often that it sounds like a joke.

A desk inside your laptop

Dan's answer starts with a desk.

Picture a desk inside your laptop. Every program you open, the browser, the email, the video call, works on that desk. It's the computer's working memory: the space where things happen right now. (Geeks call it RAM. You don't need to.)

When things are going well, programs take a bit of desk space, do their work, and tidy up after themselves. But after hours of use, some programs leave clutter behind: papers they forgot to put away. Microsoft's own documentation describes the problem. When a program keeps taking memory and never gives it back, “as memory is depleted over time, Windows slows down and may experience system failures.”

And sometimes one program gets properly tangled. It's stuck, waiting for something that will never happen, and it can hold up everything else on the desk with it. Not always: often only that one app freezes. But sometimes the whole laptop feels stuck.

The clean desk

A restart clears the whole desk. Every program closes, the working memory is wiped, and everything starts fresh, from a clean, tidy desk. Whatever got tangled is simply gone.

That's why it works so often. When nothing is actually broken, and the trouble is clutter or a tangle that built up while the computer was running, a restart sweeps it away.

“Wouldn't shutting down do the same?”

That was Liz's next question, and on Windows, the answer is: not quite.

Windows has a feature called fast startup, and it's on by default. With fast startup on, when you choose Shut down, Windows closes your programs, but tucks part of Windows itself away in a drawer, so it can start faster next time. Microsoft's documentation says the core of Windows, along with its drivers (the small programs that run your hardware), is saved rather than closed.

That's great for speed, but if the clutter was in that part of Windows, it comes right back when you turn the laptop on.

Restart is different. Microsoft says fast startup doesn't apply to Restart: it does a full startup and gives you “a completely new Windows state”. So when something's wrong, choose Restart. It's the truly fresh start.

Liz chose Restart. Her laptop came back with a minute to spare.

What a restart can't fix

A restart clears out whatever got stuck. It doesn't fix things that are actually broken. A cracked screen will still be cracked. A full disk will still be full. And if a problem comes back after every restart, the restart is hiding it, not fixing it: that's the moment to look for a different fix or ask for help.

What the video left out

Macs and phones. The video said “on Windows” on purpose. On a Mac, Apple's advice for a frozen app is to force quit it, and to restart the Mac if that doesn't help. A restart helps there for the same reason: a clean desk.

When even the screen is stuck. On Windows, press Ctrl+Alt+Delete, select the power button in the lower-right corner, and choose Restart. If nothing responds at all, the last resort is to hold the power button until the computer turns off: Microsoft says up to 20 seconds, and Apple says up to 10 seconds on a Mac.

Unsaved work. A forced restart closes everything without asking, so anything you hadn't saved can be lost. Another good reason to save often.

So a restart clears out whatever got stuck. Not a broken part, or a full disk.

What you can do

• When something's acting strange, restart before anything else. On Windows, pick Restart, not Shut down.
• Frozen screen on Windows? Ctrl+Alt+Delete, then the power button in the lower right, then Restart.
• Completely stuck? Hold the power button until it turns off (up to 20 seconds on Windows, 10 on a Mac).
• Save your work often, so a forced restart costs you nothing.
• If the same problem keeps coming back after restarts, it needs a real fix, not another restart.