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Whilst browsing the internet I found an article here about how to run a Power Efficiency Report. As I wasn't doing anything, I decided to try it and see what it did.

In the results it listed the following four sleep states with true of false next to them showing if my PC supports it.

  • S1
  • S2
  • S3
  • S4

What are the differences between these sleep states?

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  • Thanks for the answers guys. I upvoted both answers, Wil got accepted answer because he set out the answer rather than just copy+paste.
    – Connor W
    Nov 18, 2009 at 18:41

2 Answers 2

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S0 - On / Working

The computer is powered up. If supported, power conservation is handled by each device.

S1 - Sleep

CPU is stopped. RAM maintains power. Everything else is off, or in low power mode.

S2 - Sleep

CPU has no power. RAM maintains power. Everything else is off, or in low power mode.

S3 - Standby

CPU has no power. RAM maintains power, refreshes slowly. Power supply reduces power. This level might be referred to as “Save to RAM.” Windows enters this level when in standby.

S4 - Hibernate

Power to most hardware is shut off. Any files in memory are saved to the hard disk in a temporary file. If configured, the NIC will remain on for WOL, or AoL. This level is also known as “Save to disk.”

S5 - Off

Everything is off. No files are saved. If configured, the NIC will maintain power to listen for WOL (Magic) packets. This is known as a shutdown.

Source

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  • How can I know to which of them my computer is configured when sleep ?
    – Royi Namir
    Jul 10, 2014 at 7:15
  • "Sleep" will normally be S3. Some motherboards have an option to let you specify S1 or S3. S2 was rarely implemented.
    – Jamie Hanrahan
    Sep 26, 2014 at 4:16
  • It's almost certainly S3. Some systems have an option in the BIOS settings to use S1 instead of S3 for standby - this is for cases where your system won't resume properly from S3.
    – Jamie Hanrahan
    Sep 26, 2014 at 4:25
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    how does modern S0ix fit into these?
    – dimisjim
    Sep 21, 2022 at 7:36
  • I believe modern standby (S0) remains internet-connected while in sleep so the CPU still runs but maintains low power. A lot of newer computers have S0 as set as default but I think they can still be switched between S0 and S3 in the BIOS or through some hidden bootloader.
    – amitkulk123
    Feb 21 at 3:38
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Excerpt from Wikipedias article on ACPI

  • S0/Working System is on. The CPU is fully up and running; power conservation is on a per-device basis.
  • S1 Sleep System appears off. The CPU is stopped; RAM is refreshed; the system is running in a low power mode.
  • S2 Sleep System appears off. The CPU has no power; RAM is refreshed; the system is in a lower power mode than S1.
  • S3 Sleep (Standby) System appears off. The CPU has no power; RAM is in slow refresh; the power supply is in a reduced power mode. This mode is also referred to as 'Save To RAM'.
  • S4 Hibernate System appears off. The hardware is completely off, but system memory has been saved as a temporary file onto the harddisk. This mode is also referred to as 'Save To Disk'.
  • S5/Off System is off. The hardware is completely off, the operating system has shut down; nothing has been saved. Requires a complete reboot to return to the Working state.

Here's the full article

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  • I always called S3 "sayonara mode" on Windows XP because it was doubtful that the system would ever get back to S0 and work 100%. Thanks for quoting Wikipedia and saying that. +1
    – Dan Rosenstark
    Nov 18, 2009 at 9:20
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    Just one nit: Hardware is not "completely off" in S4, but power consumption should be the same as in S5. In ALL S-states (even S5) the power supply will maintain +5SB to the motherboard and, sometimes, to a few other peripherals. This permits "wake on LAN", among other things, to work. In fact, even responding to the front panel power button requires +5SB! It normally provides an amp or two at 5 volts. The only way to turn off +5SB is to either turn off the PSU with a hard power switch (some have one on the back panel) or else unplug it.
    – Jamie Hanrahan
    Sep 26, 2014 at 4:21

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