When you select “Sleep” in the power options of your Windows PC, what exactly happens? We’ll explore what it means, and whether your PC is having pleasant dreams.
Sleep mode is a low power mode
Sleep mode is different from shutting down the computer, which shuts the computer down completely. When you turn off your computer, it takes longer to restart your computer and you must first close all your programs and files.
In contrast, sleep mode is a power-saving state that allows a computer to quickly resume full-power operation (usually within several seconds) when you want to start working again. When you enter sleep mode in Windows, your PC does the following:
- The screen turns off.
- The PC stores its current state in memory.
- The PC stops sending power to most hardware devices.
- The PC enters a low power consumption state.
As long as some power continues to flow to your PC (for example, your desktop PC is still plugged into the wall or your laptop still has battery power), you won’t lose any work or the state of your machine. When you turn your computer back on, you can pick up right where you left off.
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The magic of ACPI power modes
When you use sleep mode in Windows, it’s as easy as selecting an on-screen option or pressing a button. But have you ever wondered how they work on a lower level?
Sleep mode is governed by ACPI sleep states. ACPI (Advanced Configuration and Power Interface) is a power management specification that operating systems use to control hardware power states. There are six main ACPI power states in the standard, often referred to by their abbreviations. Is it so:
- S0: Labor
- S1: Sleep
- S2: Sleep
- S3: Sleep
- S4: Hibernate
- S5: soft shutdown
S0 is the power state your PC is in when it is turned on and working normally. S1, S2 and S3 are progressively lower power states. S1 and S2 are not used very often. At S1, your PC’s CPU stops executing instructions, but it doesn’t lose power. In S2, your PC’s CPU also loses power. In S3 (often called Standby or Suspend to RAM), most of your PC’s components lose power except memory, which is kept up to date with a minimal amount of power. S3 is the most used mode (determined by your PC hardware manufacturer) when putting your PC to sleep.
S4 is the hibernation state. In this state, your PC saves the contents of its memory to a hibernation file on the hard drive and then shuts down. When you wake your PC from hibernation, it reads the hibernation file and restores your open programs and files from the hard drive. S5 is the “soft power off” state. In this state, your PC is completely powered off. It is the same as if you had pressed the power button to turn off your PC.
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How to put your PC to sleep
Now that you know what happens when you put your PC to sleep, how do you actually do it? Fortunately, it’s really easy in both Windows 10 and Windows 11. By default, on many machines, you can simply press the power button once and your PC will automatically go to sleep. If that doesn’t work, open the Start menu, click the power icon, and then select “Sleep.” Or you can press Windows + X on your keyboard, then press “U”, then “S”. Your PC will go to sleep instantly.
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