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The Macbook Pro Model MC374, MC375 from 2010 consumes only 6.6W when idle (without display) when powered with 100V to the power supply.

How can I build a modular, high-spec computer which will have similar power consumption when idle - i.e. when the system is normally running, but the user (nor any daemon on the system itself) is doing anything, just waiting for user input?

I do not care very much about the power consumption when the system is used, but I want the power consumption when CPU utilization is below 1% to be as low as possible.

I don't want the Mac, because I want the machine to be as modular as possible, preferably not a laptop, which are never too modular, but maybe some mini-ITX or even full size ATX board.

I would like to be able to have at least 4 GB RAM in the machine, preferably 8 GB or more, and for it to be a powerful computer when used, comparable in processing power to a AMD Athlon64 4000+.

Do component (motherboards, CPU, memory), from which I can build such a machine exist?

Are there any tricks like undervolting, underclocking that I can use to reduce the power consumption when idle without losing too much processing power when non-idle (losing 50% is OK)?

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closed as off topic by Canadian Luke, 8088, Journeyman Geek, Kyle, Nifle Jul 22 '12 at 17:20

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...any reason for not having the computer go to sleep when idle and have it wake on lan? Intel SpeedStep and AMD PowerNow! reduce the CPU when idle btw –  Arctor Apr 2 '11 at 0:38
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Yes, I need to be able to read what is on the screen while it is idle. I wrote about 6.6W power consumption without a display, only because I will worry about low-power display separately, it does not mean it will run without a display. –  miernik Apr 2 '11 at 0:41
    
8gb of ram will take up more than half of your w allowance. –  Sandro Dzneladze Jul 20 '12 at 12:48
    
In Super User, and all the StackExchange sites, shopping or product recommendations are considered off topic and open ended, and sometimes even too localized. Try to reword your question in a way that you are not asking for products, but more of processes; this will help keep it on topic –  Canadian Luke Jul 20 '12 at 16:28
    
do you want it to use 6w with a display, or blank the display when the user isn't entering input? –  rogerdpack Jul 20 '12 at 16:34

3 Answers 3

Since you mentioned a MacBook Pro, have you considered Apple products? Apple advertises the current Mac Mini as "the world's most energy-efficient desktop computer." See: http://www.apple.com/macmini/environment.html

Seems like it gets pretty close to what you're looking for. Idle power consumption is advertised at 9 watts.

Perhaps this won't quite work for you since you want it to be modular, but looking at the components they use for it is a good start.

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"I don't want the Mac, because I want the machine to be as modular as possible, preferably not a laptop, which are never too modular, but maybe some mini-ITX or even full size ATX board," said the question asker... –  nhinkle Apr 2 '11 at 19:39

Another strategy is to start with a processor. The fastest low-voltage processor (17W TDP) available today is Intel's i7-2657M. Going up to 25W TDP, there is the i7-2649M. All modern processors will clock-down when idle, but when you get processors that are optimized for lower TDP's, they're usually using low leakage-current transistors and will thus use less power at the same clock rate as other processors (at the expense of not being able to clock as high).

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Wow, 6.6W is pretty low even for a notebook these days.. How did you geht this number? Simple power meters may have errors in the same order of magnitude, because a switched power supply is not really a simple resistor whe you look at AC voltage and current.

Its hard to go < 30 Watts with COTS PC parts. Example: A simple 3,5" 7200RPM Hard disk drive will draw about 7 W alone, just when its platters are spinning.

That said, there are "PC" componets available that have the power-saving note- and netbook chipsets and CPUs onboard. But they are expensive and harder to get. A complete notebook may be cheaper.

The german magazine c't had an overview of current desktop CPUs, including (primary=AC) power consumtion. The lowest were the new Sandy-Bridge Intel CPUs with about 23 W idle.

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Some netbooks have 6-7W with display ON, so the measured power seems OK for IDLE. –  Turbo J Apr 2 '11 at 19:19
    
this will be without any disks with rotating things, just flash+RAM, so the power consumption of 7200RPM HDDs doesn't matter here. Basically I am looking for the lowest power consumption of motherboard+CPU+RAM+videocard in idle. BTW: I heard that undervolting the CPU can save 20% energy, did anyone hear about undervolting the whole mainboard? For example supplying 11V instead of 12V and 4.5V instead of 5V with a specially designed power supply? –  miernik Apr 2 '11 at 19:51
    
I had to replace some PSUs when their +5V dropped to +4.5V, as the mainboards got unstable. And for +12V: There are switched power supplies behind 12V, they will simply draw more current. Undervolting the CPU can be done with BIOS, STFW for that - its mainboard specific. One question remains: What are you trying to archive - what do you want to use your system for? –  Turbo J Apr 19 '11 at 23:57
    
What I am trying to achieve? Having the computer running full time (24h/day) in a van, powered from a battery recharged by from solar panels. Mobile office - computer used for web browsing, programming, everything. –  miernik Apr 20 '11 at 0:51

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