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I am wondering what the relationship is between the Sx power states and the Dx power states. E.g. when I set the display to sleep after 5 minutes and the system sleep time to 10 minutes, will the system enter the S1-S4 power states after 5 minutes or only after 10 minutes? Also, if the system sleep time is set to 5 minutes and the display sleep time to 10 minutes, will the system go to sleep after 5 or after 10 minutes? I am asking because I am writing software that will communicate with the display over DDC. If the display is sleeping (D3 mode I presume), and the system stays at S0, then communication will not be possible. I would like to catch the power events, and take appropriate actions.

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Let's define what's happening for each one:

Display Sleep means the display is powered off. The video connection from the DVI/VGA port is usually turned off, and most monitors will shut off automatically when this happens.

System Sleep is when the system itself goes to a low power mode, what you're referring to as the S1-S4 power states.

If the system is sleeping, there is no need for the display to still be on. If the system sleeps and the display is not already off, the display will be turned off. Thus, your second scenario of sleeping in 5 minutes will also turn the monitor off at 5 minutes.

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Thanks that was the answer I was looking for. I'm afraid I was a bit lost in all the documentation. –  Kurt Pattyn Dec 10 '09 at 21:31
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In my experiences, if the display is set to 5, and the computer 10, the computer wil lbe awake but display off for minutes 5-10, then both asleep. If set to Display off- 10 and computer sleep - 5, the computer will never be on while the display is off, it will just go to sleep at minute 5 (which will cause the display setting to be irrelevant)

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