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I have my home computer set to go into "sleep mode" when idle for a short time, and I assumed that by doing so I was saving lots of energy and that it was good for the computer by shutting down nearly every component while the computer is sleeping.

However, this website claims that using sleep mode "can result in more harm that good. Your memory is still fully functioning, which can lead to overheating and damage, so it's always better to fully power down and let your machine rest." and additionally, it states that it "costs about $50 more per year on your electric bill".

The website is sponsored by Bank of America and Visa, so I'd hope that they did their research, but it doesn't seem accurate, and is contrary to measurements of my own computer, which uses 1 - 2 watts in "sleep mode" (my Kill-a-Watt meter bounces between 1 and 2 Watts when measuring sleep mode power, and none of the components inside are warm to the touch).

At 1.5W, the computer should only cost around $2/year to keep it in sleep mode all day every day (at 15 cents/KWh for electricity), and 1.5W of power dissipation should not cause any heat problems at all, even with no fans running. To get up to the $50/year quoted on that website, the computer would have to dissipate nearly 40W of power while in "sleep mode."

The website dates back from Oct, 2012, but my computer is older than that, so I don't think that the information on the website is simply out of date.

Is it common for computers to use significant power in "sleep mode"? Doing so would seem to negate the entire advantage of having a sleep mode in the first place.

Granted, turning it off (or hibernating it) may be more sustainable, but I'm trying to strike a balance between usability and sustainability.

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    I can't find any other source indicating damage from sleep mode, and given their proposed $50/yr for a computer in sleep (vs. your measured $2/year) I'd say anything else on that page is suspect. – Michael Kohne Apr 8 '14 at 1:15
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    The OS matters here as well. 'Sleep' for a Mac is more akin to the Windows 'hibernate' feature than Windows 'sleep'; and uses dramatically less energy than a 'sleeping' Windows PC. (Though more than a 'Hibernating' one!) – LessPop_MoreFizz Apr 8 '14 at 13:18
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"Sleep mode" (on a computer or notebook) is a term that can hold different meaning. Generally it is considered S3 as defined by the ACPI specification, otherwise called "suspend-to-RAM," where your computer's RAM remains powered (let's call it charged) so that everything your computer is "thinking" at the time it entered sleep mode, it will resume thinking once it's awakened.

If your RAM loses power during Sleep Mode, you will lose your system's current state, which can be harmful to some data only. All running software should be able to handle the announcement that "I'm going to sleep kids!" sent by the system [including the operating system itself].

Things like "hybrid sleep" are measures to help protect this possible data loss by entering into S4 ("suspend-to-disk"), otherwise known as Hibernation before power loss occurs (it simply watches battery levels, it can't magically tell if you've unplugged the power from the back of your computer).

So, while S3 does use more power versus G2 ("soft off", what you think is actually "off", although some peripherals, such as your network port, are likely still powered), it doesn't use a great amount more, and it uses a lot less than G0 (aka "working on").

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    This is good for answering the 'wasteful' portion, but it doesn't talk anything about the 'damaging' part (which I believe is entirely bogus, but would still like proof of). – SpellingD Apr 11 '14 at 18:44
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    Thanks for the answer, this doesn't exactly debunk the website, but unless someone can point to industry standards or regulations that put a cap on power usage for each power state, then this is probably as close as I'm going to come to an answer. – Johnny Apr 11 '14 at 19:58
  • What is an isn't powered on in S3 is generally arbitrary, but must meet a minimum requirement (RAM); generally it may also include powering USB for input (to wake). The only power scaling that is standardized as voltage scaling affecting D0 and C0 as discussed on the Wikipedia previously linked. To discuss more technical portions of your question, beyond simple skepticism, you may want to consider migrating this question to superuser. – mbrownnyc Apr 14 '14 at 1:19
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Damage to the computer because of "sleeping" frequently, if it happens, is probably caused by thermal cycling. Thermal cycling is the process of expansion-contraction due to changes in temperature. Even if the temperature itself stays within the rated limit, a large number of cycles can cause fatigue in the solder joints on your computer's internal components, which causes failure. Every time you put your computer in sleep mode, it cools down, then it heats up when you turn it back on.

For example, fatigue due to thermal cycling was the primary cause of the high early failure rate of Nvidia's 8600 series line of graphics cards (Wikipedia, blog post going into more detail, in Spanish).

I qualified my initial statement because I can't find any evidence that "sleeping" frequently leads to early failure.

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    But the article suggests turning the computer off completely is better than using "sleep mode", so there'd be the exact same number of thermal cycles. – Johnny Apr 10 '14 at 23:14
  • @Johnny, You're right. I wasn't clear: my implicit comparison was between 'sleeping' the computer or leaving it on. – LmnICE May 20 '14 at 11:11
  • Frequent sleeping also implies frequent HDD spin-downs and spin-ups, which can wear the mechanical parts. – Tobia Tesan Jun 8 '16 at 17:05
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To be just as much simple to you as I can be, actually what sleep mode in computer is, that only the LCD is turned off saving a little amount of energy consumption only. Which means, that only the LCD is turned off this way. All of the other hardware components still run as they have to.

Take the example of a human. When we sleep our metabolic rate is too low that it is almost negligible, but still it isn't. His brain works, heart beats, only thing that isn't doing its job is his eyes and some other organs (biology student would have explained it in a better way, I am just a Computer Science student now). This way, less energy is required to make his body work.

Now the computer also takes up energy and provides it to other parts of the hardware for them to run. In Sleep Mode, computer's mind (CPU) works, clock ticks are being generated, RAM works and all other components run, so that you get back to the exact place where you left off just with a press of button (or pick of a lid on laptops). This way, LCD is turned off only and the computer goes to sleep mode. You can imagine how much energy would be saved by turning off this hardware, these components get turned off:

  1. VGA card

    • In some of the VGA cards there are CPUs.
    • RAM of the VGA card.
  2. LCD screen

You can get some information from this website, where it has been shared which component of your computer drains most of the energy of your computer. http://lifehacker.com/5566020/how-to-maximize-the-battery-life-of-your-windows-laptop

So, you can save energy by going into sleep mode and you can save your time by coming back online from a sleep mode.

Back effects

The only bad effect of the sleep mode, I have myself faced is that it gets heat up too soon. You can never even imagine when it would make your VGA card melt down due to heating.

One other negative point is that the laptop will still be consuming a small amount of battery while in sleep mode.

and finally - Some system processes and applications end up hogging resources and the only way to release it is to restart.

So, you can never say which thing is good or bad. There are some bright and some bad effects of every process.

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    Please show us a modern (i.e. 2010+) computer where "sleep mode" is not either suspend-to-ram or suspend-to-disk. – Martin Schröder Apr 17 '14 at 22:12

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