What do sleep, shut down and restart do?

What happens when you put your computer to sleep? What's the difference between restarting your computer, shutting it down, and turning it back on?

Sleep

When you put your computer to sleep, it goes into low-power mode. In this mode, the display turns off, your computer saves its current state (open files or browser tabs, etc.) to memory, and it stops sending power to most hardware. As long as your computer is getting power, when you turn it back on, it will start up instantly, and look just like it did when you put it into sleep mode.

This feature is handy on laptops, especially when you need to move from one location to another (from a meeting back to your desk, maybe) but you don't need to restart your computer.

All computers implement sleep similarly, using the Advanced Configuration and Power Interface (ACPI) standard. The ACPI is how computers "know" what sleep is.

There are six power states in the ACPI, S0 through S5. But we only use three of the ACPI power states. S0 is, confusingly, the power state when your computer is on and running normally. S3 is the most used Sleep mode. S4 is the hibernate mode, and S5, also known as a "soft off," happens when your computer has no power at all.

We can confuse Hibernate with Sleep. When your computer hibernates, all the details of the running computer get written into a particular file, and the computer gets powered down. When the computer gets turned back on, it reads the hibernate file and puts everything back the way it was. Choosing to sleep over hibernate results in a much faster start-up time, but you can't use sleep when the computer is going to be powered down.

Shut down

Since Windows 8, when you click Shut down, your computer closes all your open files and programs and powers down your computer.

Restart

Restart does what it says, it turns your computer off and then turns it back on again. Since Windows 8, Restart does something that shutting down doesn't. Well, other than turning your computer back on.

All versions of Windows since Windows 8 have a feature called Fast Start that helps the computer start up faster. When you shut down your computer, it closes your programs and files and writes the Windows kernel to disk so the computer will start up faster.

Restarting your computer doesn't use Fast Start. Restart closes all your programs and files and ends all running Windows processes. Giving you a clean Windows kernel when your computer starts back up. That's why restarting is required when programs misbehave or updates need to be installed.

And yes, if you're troubleshooting something on your computer, restarting is the same as rebooting. What if it all goes horribly wrong and all you can do is hold down the power button to get the thing shut off? That's the same as restarting since Windows didn't write the kernel to disk before losing power.

Funny, because it's true

Whoever said that the definition of insanity is doing the same thing over and over again and expecting different results has obviously never had to reboot a computer.

Do you have a computer or technology question? Greg Cunningham has been providing Tehachapi with on-site PC and network services since 2007. Email Greg at [email protected].