Introduction

Anyone building a computer system should eventually pose the question: How much power does the system actually require? This is an important consideration, since it's impossible to choose an appropriate power supply without actually knowing the demands of your system. Unfortunately, many users take the easy way out: just grab a 500W power supply and call it good. If you really want to be safe, you can even grab on 800W PSU... or if you plan to run multiple graphics cards perhaps you really need a 1000W unit, right?

If people really took the time to examine system power requirements, we would see a tremendous increase in sales of 300W to 400W PSUs. The truth is that the vast majority of systems would run optimally with such a "small" power supply. Even if you're running SLI/CrossFire, you don't actually need a 750W power supply. (Of course, we recommend purchasing a good quality power supply, as there are certainly "750W" PSUs out there that can't reliably deliver anywhere near that much power.) To help dispel some myths relating to power requirements, we've put together a couple of charts.

GPU Power Consumption*
Manufacturer Idle Load
NVIDIA GeForce 9600 GT 49W 107W
NVIDIA GeForce 8800 GT 64W 115W
NVIDIA GeForce 9800 GTX 79W 116W
NVIDIA GeForce 9800 GX2 90W 179W
NVIDIA GeForce 8800 Ultra 100W 186W
ATI Radeon HD 3650 17W 32W
ATI Radeon HD 3850 53W 82W
ATI Radeon HD 3870 62W 92W
ATI Radeon HD 2900 XT 67W 104W
ATI Radeon HD 3870X2 55W 130W

* Actual power consumption for the graphics cards only. Results taken at idle on the Windows desktop and under full load running the Fur benchmark.

CPU Power Consumption**
Manufacturer Idle (EIST or CnQ Enabled) Idle Load
Intel Core 2 Duo E4500 14W 17W 36W
Intel Core 2 Duo E8500 18W 22W 43W
Intel Core 2 Quad Q9550 19W 23W 60W
Intel Core 2 Extreme QX6850 29W 32W 103W
Intel Core 2 Extreme QX9770 26W 56W 86W
AMD Athlon 64 X2 5000+ 33W 47W 89W
AMD Athlon 64 X2 6000+ 25W 74W 160W
AMD Phenom X3 8750 50W 67W 86W
AMD Phenom X4 9600 BE 29W 36W 101W
AMD Phenom X4 9850 BE 38W 53W 126W

** Actual power consumption for just the processor. Results taken at idle on the Windows desktop with either EIST/C&Q enabled or disabled, and full load generated using BOINC.

Chipset/Motherboard Power Consumption***
Platform and Chipset Load
Intel P35 (775) 37W
Intel P965 (775) 39W
Intel X38 (775) 52W
Intel X48 (775) 40W
NVIDIA 680i (775) 46W
NVIDIA 790i (775) 51W
NVIDIA 750i (775) 59W
NVIDIA 780i (775) 69W
NVIDIA 8200 (775) 29W
AMD 690G (AM2) 34W
AMD X3200 (AM2) 35W
AMD 770 (AM2) 40W
NVIDIA 570 (AM2) 40W
AMD 790FX (AM2) 42W
AMD 790X (AM2) 43W

*** Actual power consumption for the motherboard and chipset. Idle and load power do not differ by any significant amount.

Top-end graphics cards are clearly one of the most demanding components when it comes to power requirements in today's systems. Only heavily overclocked CPUs even come close to the same wattages. Note that the above chart only includes last generation cards; NVIDIA's latest GTX 280 requires even more power.

Looking at the processor side of the equation, Intel's Core 2 Duo/Quad/Extreme CPUs in general have very low power requirements. AMD's latest Phenom processors aren't far behind, however, especially in light of the fact that they include the memory controller rather than delegating the task to the chipset. We should also mention that part of the reason for the extreme power requirements on the X2 6000+ come from the use of an older 90nm process.

Naturally, motherboards also require a fair amount of power. Current motherboards average around 47W for socket 775 and 39W for socket AM2/AM2+, but features and other factors can heavily influence that number. Outside of their IGP solution, NVIDIA's chipsets tend to use more power than the competition; AMD chipsets on the other hand typically require less power. Again, numerous other aspects of any particular motherboard will impact the actual power requirements, including BIOS tuning options.

Hard drives and optical drives account for another 10 to 20W each. However, remember that hard drives are a relatively constant 10 to 15W of power draw (average is around 12W) since the platters are always spinning (i.e. idle), and movement of the drive heads during read/write operations (i.e. load) only increases power draw slightly. Optical drives on the other hand stop spinning when idle, requiring only about 5W, while during read or write operations they need around 18W.

RAM power requirements measured a constant 2W per DIMM, regardless of capacity (though clearly not including FB-DIMMs). That figure is estimated, unfortunately, as we could not measure DIMM power requirements directly; we measured power draw with two DIMMs and then again with four DIMMs to arrive at the reported figures. It's also not possible to easily separate memory power requirements from the motherboard and chipset, as they share many of the same power connections from the PSU.

Building Three Sample Systems
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  • JarredWalton - Monday, September 22, 2008 - link

    Edit: Christoph's text reflect the range for 90VAC to 230VAC, but my editing made that a little less clear. I've added in "input voltage" comments to clarify things. Reply
  • poohbear - Monday, September 22, 2008 - link

    thanks for this article!!! im planning on running 2 8800gt's in SLI on a 80% efficient enermax 420wt psu. it has 29a on the 12v+ line so im confident it can run it. All this BS about needing 500+wts psus is nonsense if you know your cards power needs. Reply
  • bela - Monday, September 22, 2008 - link

    Where did you get those power figures? Dream last night or what?

    This is totally made up bullshit.

    The ANTI-AMD war continues @ Anandtech

    you compare 2 year old 90nm AMD DC with new 45nm Intel DC, is that a fair peer group?

    6000+ 160W load? Even with 90nm this ist ridicoulus, it should be around 110W, a new 65nm 6000+ needs less then 80 Watt, a 65nm 5000+ less then 60W, so talk about making Intel look good.
    Reply
  • elaar - Monday, September 22, 2008 - link

    bela, you seem to be incredibly rude and have also missed the entire point of the article, if it makes you that annoyed then why not do us all a favour and stop reading articles and commenting in the future.

    I for one found the article incredibly useful especially when you consider the sheer number of people who go out and buy way too powerful psu's and have no idea what they're doing.

    It doesn't matter what processor or graphics cards power stats were listed, they were just there as examples for the article, god knows how you've managed to get so confused with paranoia to believe it was an anti AMD campaign.

    Thanks Anandtech for a superb article.
    Reply
  • npp - Monday, September 22, 2008 - link

    The power draw figures for the X2 6000+ are a bit off-scale (and yes, it is an older 90nm die, apparently), it's a tiny bit, however. You can have a look at the charts here (damn, the stupid link button doesn't work):

    http://xbitlabs.com/articles/cpu/display/dualcore-...">http://xbitlabs.com/articles/cpu/display/dualcore-...

    The system equiped with an X2 6000+ was measured to draw about 304W at full load and 180W at idle. Adding ~25W to that difference makes for ~150 total power consumption, which comes close to what was stated in the article. Just because you thought "it should be around 110W" doesn't make you automaticaly right. Learn living with the truth and stop behaving like a small child.

    Furthermore, as it was properly stated, those figures were intended to draw a frame around the best and worst case scenarios, representing some of the CPUs typicaly found in a system today. They weren't meant as a CPU-to-CPU comparison.

    That old dark sense of anti-AMD or anti-Intel paranoia continues to be abundant in every discussion nowadays... What a triumph for the PR brainwashers at both camps.
    Reply
  • bela - Friday, September 26, 2008 - link

    No, they are not of scale, they are bullshit, nothing else but made up numbers.

    Look at this:

    X2 6400+ WITH Voltage Regulator, depending on Board 85,9 or 103,3 Watt


    http://ht4u.net/reviews/2008/amd_phenom_leistungsa...">http://ht4u.net/reviews/2008/amd_phenom_leistungsa...

    This ist the truth, nothing else
    Reply
  • Kiijibari - Monday, September 22, 2008 - link

    Could this be a typo ?
    106W is ok, 160W is a little bit out of the "normal" scale ..

    Furthermore .. which 6000+ is it ?

    There are 3 different models:

    one 90nm "normal" model: 125W 3,0 GHz; 2x1MB L2 (ADX6000IAA6CZ)
    one 90nm EE model: 89W 3,0 GHz; 2x1MB L2 (ADA6000IAA6CZ)
    one 65nm model: 89W 3,1 GHz; 2x512kB L2 Cache (ADV6000IAA5DO)

    cheers

    Kiiji
    Reply
  • JPForums - Monday, September 22, 2008 - link

    This is a curiosity for me as well.
    I have an A64 X2 6400+ 125W, 3.2GHz, 2x1MB L2 (don't remember the model number off hand) that doesn't seem to require near that power.

    The 6400+ is running on an nForce 570SLI with 8Gb (4x2Gb) DDR2-800.
    The video card is an 8800GTS 512Mb.
    I have 4 HDDs 2 optical drives and 8 fans (7 case + CPU fan) that according to specifications run at 8.6W when at full speed (how I have them while gaming).
    If I use the (presumably lower) power ratings used for the 6000+ and the 8800GT, and I exclude the power of usb components and the fan controller/sensor overhead, my total system consumption at load (using the values from the article) is around 450W.

    The curiosity is that the same Enermax Pro82+ 385W PSU mentioned in the article has no issue running this system. (Ironically emphasizing the point of the article) Using a basic kill-a-watt meter, I found a power draw of 378.2 was as high as it got during benchmarking, gaming, stressing the system. For reference, I tried 3DMarks 2006/Vantage, Stalker, Crysis, C&C3, and a combination of 2xPrime95 + ATItool's GPU heat up mode (rotating fuzzy block). The ATI tool combo offered the largest power draw in my system. Granted, the kill-a-watt may not be as accurate and I may not have stressed the system as well as in the article, but I suspect the power draw numbers for the 6000+ are lower than the article suggests.

    That small inconsistency aside, this was a nice article. I would like to see those power draw blocks that you overlayed on the power efficiency and noise curves included in future PSU reviews. It would be a quick and easy way to let people know how applicable the PSU being reviewed is to them. It would also be interesting to see how high the power draw gets with water cooling systems, case mods (I.E. cold cathodes), and the likes.
    Reply
  • Christoph Katzer - Monday, September 22, 2008 - link

    My 6000+ was 90nm, yours? Reply
  • Kiijibari - Monday, September 22, 2008 - link

    He has a 6400+, that CPU is 90nm only (so far).

    But he has a AM2 mainboard, maybe you had a AM2+ board, and the onboard VRMs are running badly with a AM2 CPU ?

    cheers

    Kiiji
    Reply

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