Many people say they use Hibernate instead of Sleep mode because Hibernate draws no power. Unfortunately, when it comes to desktop PCs, they’re wrong. Desktop PCs still use some power even while they’re shut down.

Laptops generally don’t use any power while shut down or hibernating, as that would cause unnecessary battery drain. Desktop computers don’t have to worry about batteries, so they’re generally a bit more power-hungry.

Sleep, Hibernate, and Shut Down Defined

RELATED: What's the Difference Between Sleep and Hibernate in Windows?

When you use Sleep mode, your computer continues providing power to its RAM. The RAM contains your computer’s working memory and requires constant power or it will forget its contents. Sleep mode continues providing this power, allowing a sleeping PC to wake up almost instantly. While in sleep mode, desktop computers and some laptops have an LED that stays on, so that’s another source of power consumption.

When you use Hibernate mode, your computer saves the contents of its RAM to its hard drive and “powers off.” When you boot it back up, it will read the previous contents of the RAM from the hard drive and restore them to RAM. This may or may not be faster than a normal boot-up process, but it allows you to maintain your system state including all your open programs and documents. Because the computer doesn’t have to provide power to its RAM, Hibernate mode uses less power.

When you shut down your computer, it discards the current system state and powers off. When you boot it back up again, it has to go through the typical boot-up process, initializing hardware drivers, loading startup programs, and so on.

On a laptop, hibernate and shut down states won’t use any power, ensuring the laptop won’t waste battery power. Desktop PCs don’t have to worry about batteries, so they’ll probably draw some power anyway.

Why a Computer Uses Power in Hibernate Mode or While Shut Down

It’s clear why a computer would use power in Sleep mode — the RAM needs to draw power, of course. It’s often clear that a computer is in sleep mode because an LED is on. When a computer hibernates or shuts down, it looks off — and it basically is, but it may still be drawing power.

There are a few reasons why a computer will be drawing power in Hibernate mode or while shut down:

  • Wake on Keyboard or Mouse: Many computers will wake up from hibernate when you press a button on your keyboard or move the mouse. To do this, they have to keep their USB ports powered on, waiting for keyboard and mouse input events.
  • Wake-on-LAN: The Wake-on-LAN feature allows a computer to be woken up — even if it’s shut down — by receiving  a special type of data packet over a wired network. This isn’t something a typical home user will need, but it may be used on larger networks. To enable this feature, the computer has to keep the Ethernet port powered on and listening for the packet, even while the rest of the computer is shut off.
  • Trickle Power: If you look inside your PC’s case while it’s plugged in, you’ll likely see things using power even while it’s shut off. You may see an LED on the motherboard that stays powered and an LED on the Ethernet port that flashes as the system listens for those wake-on-LAN packets.

If you have an electricity usage monitor that lets you measure power draw, you can test this. Plug your desktop computer into the power meter, and then try both sleep and hibernate. Hibernate mode will use some power — there’s a continuum of power usage here. Different PCs will use different amounts of power.

RELATED: What Is Wake-on-LAN, and How Do I Enable It?

Reducing Computer Power Consumption

With a laptop, reducing power usage is as simple as hibernating or shutting down when you’re not using your laptop for long periods of time.

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With a desktop, there are several clear ways you can prevent it from using power. You can turn the computer off by flicking the main power switch located on the power supply — you’ll find it on the back of most traditional desktop PC towers. This switch cuts power to the computer’s power supply, so there won’t be power draw. If you want something more convenient, you can just plug the desktop PC into a power strip — you are using a surge protector that provides a power strip, aren’t you? — and power off the surge protector when you’re not using your PC. This set-up would also allow you to easily cut power to your other electronics, preventing any “phantom load” caused by devices staying in standby mode.

You may also be able to head into your computer’s BIOS or UEFI settings screen and disable Wake-on-LAN if you never use it. This will cause your computer to draw a little bit less power while it’s shut down.

Wake-on-LAN and the other features here don’t use a huge amount of power, but they do use some power. That’s why they’re generally disabled on laptops — to prevent unnecessary battery drain.

Image Credit: Michelle Hawkins-Thiel on Flickr, Dennis Vu on Flickr

Profile Photo for Chris Hoffman Chris Hoffman
Chris Hoffman is Editor-in-Chief of How-To Geek. He's written about technology for over a decade and was a PCWorld columnist for two years. Chris has written for The New York Times and Reader's Digest, been interviewed as a technology expert on TV stations like Miami's NBC 6, and had his work covered by news outlets like the BBC. Since 2011, Chris has written over 2,000 articles that have been read more than one billion times---and that's just here at How-To Geek.
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