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Maximum Efficiency: Build A 25W Performance PC Using Core i5

Maximum Efficiency: Build A 25W Performance PC Using Core i5

Back in late 2008, we ran an article showing how an efficient power supply, low-end motherboard, and entry-level Core 2 Duo could reach less than 40W system idle power. Then we took the test config and proved that a Core 2 system provides power consumption similar to that of a cheap, Atom-based desktop solution, even busting Atom in performance per watt. The introduction of the Core i5/i3 Clarkdale dual-cores with the H55/H57 chipset and on-package integrated graphics marks the next step. Systems at 30W and less are now within reach for everyone. We wanted to go even lower this time around and set 25W as the target—but at zero compromise.

Why Do I Care?

I should clarify that (apart from a discussion about global environment concerns) there's no urgent need to achieve the lowest power consumption possible on your desktop PC. This is is an optional and voluntary item. An average desktop PC requires between 45W and 60W, as long as it's employing integrated graphics and mainstream components. If you add powerful graphics and more capable hardware, you'll be at 80W and up. In this context, 50W is perfectly okay for a modern PC without serious 3D graphics. But why not pay attention to system power if it doesn't cost anything or jeopardize performance or features?

A 30W (versus 50W or higher) system idle power draw will mean only small savings on your energy bill, but it will introduce some added advantages. The most important of these certainly is the drop in required cooling. A 30W idle translates into slower-spinning fans, both on the processor and throughout the system. Another direct advantage is lower noise levels, as temperature controlled coolers have less work to do. Even passively-cooled PCs are clearly within range at 30W, although such systems typically come at a price premium.

25W PC Idle Power

Reaching almost 30W system-wide idle power was possible with Core 2 Duo when using a motherboard with integrated graphics and an efficient power supply. Of course, such a system could only deliver mainstream performance, and almost always entailed a reduced feature set. For example, G31 integrated graphics might only sip a few watts, but the IGP was already old fashioned at the time of our original article.

Today’s 25W idle power target is obtainable thanks to the new Core i3/i5 Clardale-based processors and the H55/H57 chipset. This platform offers the best overall efficiency today. With additional measures, such as slight undervolting or smart component choices, we could actually go even lower. However, it's amazing that we can reach such low system power without jeopardizing performance or features.

Naturally, you won’t get quad-core performance and 3D graphics horsepower; we’re talking about mainstream components, the performance you'd expect from a dual-core CPU, and premium features. Let’s have a look at no-compromise computing at unbelievably low power.

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  • 1 Hide
    mi1ez , 23 February 2010 15:25
    Interesting article. good work on getting down so low, would love to see it with the SSD regardless of price (and by your own admission the CPU itself is overpriced anyway)
  • 0 Hide
    Anonymous , 23 February 2010 19:04
    "For average users, it becomes relevant if you want to go for a low noise system, or if you intend to pair high performance with the lowest possible acoustic footprint."

    Why not also if a user wishes to reduce energy consumption for whatever reason, up to and including reducing CO2 emissions?


  • 3 Hide
    raotor , 24 February 2010 15:48
    I've found that the best trick to saving power during idle time is flicking that thing called the power switch to the "off" position!
  • 3 Hide
    raotor , 24 February 2010 15:49
    I've found that the best trick to saving power during idle time is flicking that thing called the power switch to the "off" position!
  • 3 Hide
    rdhir , 24 February 2010 17:43
    Would be nice to see such a comparison with one of the "Pico PSUs" for miniITX systems. They can be used in systems like this assuming cable lengths allow. They will supply up to 120W depending on model and power brick used. Most boards I believe will work with only a 20 pin power supply and you can easily buy a molex to P4 adapter.

    As this uses a 12V PSU and converts all the voltages it should be fairly efficient as this is the new trend for efficient ATX powersupplies eg Seasonic X series.
  • 0 Hide
    Anonymous , 24 February 2010 19:59
    It seems a bit strange to me that an article based on low power consumption would involve the clarkedale CPU with the highest TDP of all of them.

    But, I guess that's where the performance per watt section comes in.
  • 0 Hide
    kyzar , 24 February 2010 20:43
    Would be interesting to see how low an AMD system would go and then do a comparison of how long both systems would have to run idle to recoup the extra cost of the Intel system.

    I'm looking to rebuild my linux server at home - which has to be on 24/7 (it's an email and web server amongst many other roles), but spends much time idle. My natural inclination would be a dual-core AMD build, but the I5 does give some impressive numbers...
  • 0 Hide
    Anonymous , 25 February 2010 05:19
    I had a system which consumed 65 Watts at idle, and the only additional was a really huge passive CPU cooler, and that I have left the case open :) 

    that small PSU with that small evil fan looks really bad to me, I had once trouble with it, and really I lost my fate in that kind of PSU
  • 0 Hide
    andybird123 , 25 February 2010 16:13
    so in the first paragraph you talk about reducing power without sacrificing performance, and then you install a 5400rpm hard disk... hmmm
  • 1 Hide
    bv90andy , 27 February 2010 07:01
    In google shop this thing would cost ~660$ 430$... why would I buy such an expensive PC to keep it on idle? pretty useless
  • 2 Hide
    HedRat , 2 March 2010 22:47
    I was interested in the article at first, but must agree with some of the other comments. Not "compromising on performance"? No dedicated graphics card, prepared to switch to single-channel on the RAM and then suddenly cost is a factor when considering a SSD drive - why don't you just buy the Atom PC???!!!

    The article needed a clearer focus.
  • 0 Hide
    NickTulett , 4 March 2010 18:40
    Anyone working from home in a cold climate is going to replace the lost heat from the PC by turning up the thermostat (or knitting a jumper), so it's swings and roundabouts on the environmental front.

    As for me, I have a web and mail server (among other things) running on a 5W Sheevaplug that cost less than a ton to buy - so 25W and 300 quid isn't that tempting.
  • 0 Hide
    Mitche01 , 4 March 2010 20:40
    I know THG prefers uATX or DTX but i still like mini-itx for lower power PCing. Cost of Mini-itx mobos with embedded C7 processors is V tempting. even better if using an intel ATOM processor.
  • 0 Hide
    mi1ez , 4 March 2010 21:10
    I know THG prefers uATX or DTX but i still like mini-itx for lower power PCing. Cost of Mini-itx mobos with embedded C7 processors is V tempting. even better if using an intel ATOM processor.

    Forget Atom, the Zotac mITX boards for LGA1156 are the way forward! Ultimate modding machines!
  • 0 Hide
    Mitche01 , 4 March 2010 22:46
    While I agree the Zotec 1156 and even 775 Mobos are good, the LGA1156 is still going to use a lot of power 73W is minimum for i3, i5 or i7 CPUs. The Atom N330 dual core 1.66Ghz has a TDP of 8W! Even if you go for the low power like this article states you still cant beat 8W!
  • 1 Hide
    mi1ez , 5 March 2010 16:06
    Yeah, if I were to do mITX, I wouldn't be looking at power, more at modding a PC to fit inside something ridiculous!
  • 0 Hide
    col musstard , 22 March 2010 23:01
    im liking the bus speed and the core speed at .888v