Building Three Sample Systems

Okay, so far we have some basic power guidelines in place. Let's put these figures into practice and look at some actual system power requirements. We've selected components for three different systems, so let's examine how much power each one requires.

System 1:
Intel Core 2 Duo E4500, 4GB Memory, P35 chipset motherboard, ATI Radeon HD 3650, an optical drive, and one hard drive. Outside of perhaps the memory, this is representative of your modern entry-level computer system. At idle, this computer requires around 90W of power. Even when we put the pedal to the metal and put a full load on the graphics card, processor, and optical drive, we still have a total power consumption of only 140W.

System 2:
AMD Phenom X4 9850 BE, 4GB Memory, AMD 790X Chipset, ATI Radeon HD 3870X2, an optical drive, and two hard drives. Our midrange system roughly doubles our power requirements, and depending on the benchmark it will offer more than twice the performance of our entry-level machine. At idle with Cool & Quiet enabled, this system uses almost 168W of power, while it needs at most 341W when fully loaded.

System 3:
Intel Core 2 Extreme QX6850, 4GB Memory, NVIDIA 780i Chipset, NVIDIA GeForce 8800 Ultra SLI, an optical drive, and four hard drives. For our third example, we chose some of the most demanding products for testing. In particular, the 780i Chipset from NVIDIA has the highest power consumption of all chipsets we've tested so far, drawing a constant 69W. (There is of course some variation in power consumption even from chips of the same family, and the features and extra chips on each motherboard differ from manufacturer to manufacturer. Our particular 780i is an EVGA motherboard.) The idle power consumption for this setup is around 310W, and once we place of full load on everything power consumption increases to 544W.

Worth mention is that the second graphics card in an SLI/CrossFire setup never actually uses 100% of the theoretical maximum power consumption. We estimate power consumption based on the figures on page one, and the second GPU only runs at around 50% power at the desktop (i.e. half the idle power draw); adding a third GPU would result in an even lower load, since the third card is frequently underutilized. Likewise getting a full load on quad-core CPUs and multiple GPUs is not a typical scenario. It may be possible to draw slightly more power, but the above guidelines should suffice.

Do these numbers help clarify the situation? The first system has very low demands, and yet if we look at the PC market as a whole 90% of current shipping systems don't even provide the same level of hardware as system one. Even with that fact accepted, the question remains: what sort of power supply should you choose for such a system?

That's the next topic of discussion, and we want to show some simple ways to help you choose the correct power supply for your needs. For the moment will put aside other important factors like DC output stability, ripple and noise, and overall quality and focus on choosing an appropriate power supply. Key factors in this decision will be the efficiency curves and noise levels.

Index Efficiency Explained


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  • JarredWalton - Monday, September 22, 2008 - link

    If you look at all the included components, it should be pretty clear that the latest parts won't be drastically different from the tested components. Sure, 4870 might use 30W more (or 30W less) than the 3870, and the P45 might use +/-10W relative to the P35. Does that really change anything with the information the article conveys? I don't think so. Midrange PCs are still going to use 150-250W for the most part, whether with last year's components or with the latest stuff. If you want to look at the top-end, then GTX 280 will use more power than the listed GPUs, but even then you're not going to break 600W without overclocking. Reply
  • Martimus - Tuesday, September 23, 2008 - link

    Thanks. I have since calculated out what is needed for the processor and chipset (for a E8400 and P45 MB) and it came to about 8A. I went on the AMD website to find what the current draw was from the 4870. It doesn't say, but does recommend a 500W PSU. I am a little concerned though, because the EA500 isn't on their approved PSU list from Antec, and I have had issues with their power supplies before, plus they only have 17A available on each rail. that should be fine, but I would like to make sure I am not loading the 12V rail too heavily as well. If those components don't work (those are my plan for the moment), then I can always adjust, but I would like to have that peace of mind before I make the purchases. (the computer is a present, and I bought the Sonata III to save money because I heard good things about the Earthwatts brand, but now I am starting to get worried about this particular model.) Reply
  • Matt Campbell - Monday, September 22, 2008 - link

    I would also point out that in addition to all of the data Christoph has pulled together, we have some power consumption numbers on overclocked systems with GTX 280s as well, which seems to be one area people are asking for.

    4.0 GHz QX9770 with SLI GTX 280s: 579W Max
    4.0 GHz QX9650 with Triple 8800 Ultras: 671W Max
  • JarredWalton - Monday, September 22, 2008 - link

    Those figures are power at the outlet, though, right? And they're not tested in the same fashion as what Christoph did. Still, if you max out at 671W at the outlet, even with 88% efficiency you're only using 590W - nowhere near 1200W, which is what NVIDIA certifies for 3-way SLI. Quality over quantity, naturally, but there really aren't many terrible 1000W PSUs out there (which is why they all cost over $200). Reply
  • Torched - Monday, September 22, 2008 - link

    For all the hullabaloo about the 12v Rail why nor just recommend a PS that has a single rail. More and more manufacturers are going in that direction anyways since it eliminates the whole power trapping issue. Reply
  • gramboh - Monday, September 22, 2008 - link

    Good article. The underlying point is that you do not need 1000-1500W PSUs to run your system like I see many people claiming you do for SLI setups. I see lots of people with 700-800W PSUs with one graphics card. Insane.

    I've been running a Corsair HX520 (520W) for a year and a half now. My current config is:

    Asus P5B-Deluxe (P965) mobo
    Q6700 G0 @ 3.3GHz (1.42v actual voltage reported by Speedfan)
    4x1GB PC2-6400 DDR2 memory
    EVGA GTX280 video card overclocked (675-1350-2422)
    3 hard drives (7200.11 1TB + 2x 7200.10 500GB)
    1 optical (18x Samsung DVDRW SATA)
    3 case fans ~1500rpm + CPU fan 1200rpm
    SB X-Fi XtremeGamer audio

    Zero issues and I'm sure I have headroom to spare. Some people on forums told me I should upgrade my PSU to at least a 650W Corsair or 750-800 of other brands to run the 6700/GTX280, just goes to show people have fallen for the marketing hype of PSUs.
  • cesthree - Monday, September 22, 2008 - link

    I have had a few different systems in the last 6 months. Using the Zalman MFC-2 I can see the wattage being used in real-time. How accurate it is, I do not know, but it gets me in the ballpark.

    All systems have had the same 4 WD1600YS HDD, Lite-On DVD burner, 700W OCZ GameXStream PSU, and OCZ DDR3 1333Mhz 2x1 GB RAM. I also run 4 x 120mm fans including the one mounted to my TRUE-120.


    1. EVGA 790i Ultra (JUNK) w/ Q6600 @ 3.2Ghz 1.35VCORE, 1400Mhz FSB, 8800GTS 320MB SLI
    Idle Load: 225W, Prime Load: 275W, 3DMARK06: 325W.
    Never saw higher than 400-425W during highest loads.

    2. DFI X48-T3RS (PWNING 790i ULTRA) w/ Q6600 @ 3.0Ghz 1.32VCORE, 1333Mhz FSB, EVGA 9800GTX
    Idle Load: 200W, Prime Load: 250W, 3DMARK06: 290W.
    Never saw higher than 350-375W during highest loads.

    3. DFI X48-T3RS w/ E8400 @ 3.0Ghz 1.245VCORE, 1333MHZ FSB, EVGA 9800GTX
    Idle Load: 175W, Prime Load: 200W, 3DMARK06: 250W.
    Never saw higher than 300-325W during highest loads.

    BTW, all Watts are averages. Prime Load is averages between blend testing and small FFT's.

    I really like the meter on the MFC-2. If it is at all accurate, then it supports the logic that it isn't always necessary to have a 2000KW PSU.

    I could see needing a higher wattage, QUALITY PSU, for CF or SLI + the latest GPU'S, non-extreme CPU, with everything OC'd 25-50%, and maybe a single loop WC as well.

    Just my 2 cents.
  • Spacecomber - Monday, September 22, 2008 - link

    I was wondering if it might have been helpful to add some comments on the importance (or not) or having 8-pin 12-volt motherboard connectors, instead of the more standard 4-pin motherboard connector. I don't think that this motherboard connector, which I think largely powers the CPU, was given much attention relative to the discussion of the additional 4-pin connector for the main motherboard connector (20 + 4) and the PCI-E power connectors.

    Overall, this was a very good article. I like how it places technical details about power supplies into a context of everyday use.
  • CSMR - Monday, September 22, 2008 - link

    The power consumption data on page 1 is completely overblown.
    The tables claim to represent actual power consumption of processors and chipsets but the figures are completely exaggerated.

    There are even people who run whole systems on one or two of the chipsets listed on less power than the power the article claims for just the chipset.

    Here are actual CPU measurements from behardware and xbitlabs:">">

    I haven't seen measurements of chipset power but here is a list of TDPs:">

    Must fix this soon as Anand needs to keep its reputation for good information.
  • Zoatebix - Monday, September 22, 2008 - link

    Seriously. This guy didn't go too far our of his way to make a 30-40 watt system:"> Reply

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