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Total system power consumption

Last response: in Components
September 18, 2009 2:02:09 AM

I'm trying to build a system with 250W psu. The system will only do CPU load and some occasional heavy hard drive work (no need for fancy GPU, DVD drive). While trying to figure out whether an i7 920 (I can use hyper-threading) or i5 750 system can fit, I've realized that the total system power consumption under CPU load is different in various tests.
For instance, AnandTech shows203W for the i7:

Tom's hardware shows 318W:

Tom's hardware measurement is taken at the AC input, so given an estimation of 85% PSU efficiency their 318W becomes 270W. This is still 35% more then AnandTech measurement/ Note that GPU was idle in bothe tests.

Can anyone guess what could be the reasons for such a difference ? Do you think I can build an i7 920 system that consumes less then 250W at full CPU load ? What about i5 750 ?

More about : total system power consumption

a c 248 ) Power supply
a b à CPUs
September 18, 2009 3:20:00 AM

That's easy. Different test criteria and different benchmarks. For example, in the Tom's Hardware article the enthusiast's system was equipped with two BFG GeForce GTX 260 OC video cards operating in dual SLI mode for all of the tests. The Anandtech system was equipped with one eVGA GeForce GTX 280 video card.

NOTE - For the Crysis Warhead and FarCry 2 benchmarks Anandtech tried two different mutiple video card configurations - one with a pair of EVGA GeForce GTX 275s and another with a pair of Sapphire Radeon HD 4870 X2s.

That's one of the problems we have. It is not unusual to see different results because there is no international standard for testing power consumption. I have found only one site that can actually measure the power consumption of individual components. The reviewer uses an electronic measuring device that is connected between a power supply and the individual pc components. Just about all of the other sites use total psu draw at the wall outlet and some try to extrapolate that into gpu usage.

I think every single technical review I have read used a system with one and sometimes two video cards instead of onboard graphics. I have no basis for rendering an opinion as to whether a 250 watt psu could power a simple Core i7 or Core i5 system that does not have a video card. My inclination would be to say no.
September 18, 2009 6:07:48 PM

I think a top quality 250watts 80plus certified power supply could handle the following specs:

Intel Core2 Quad (65w series,42112,40814... )
G45 chipset motherboard (around 30-35w TDP, depending on models)
3.5” Samsung EcoGreen/ WD Caviar Green hard drive (6-7 watts ).
Memory (5-6 watts -source not reliable-)

CPU and case fans (depends on cooling method )
USB usage (keyboard,mouse ??)
No graphics card required (on board X4500HD graphics and sound )


I doubt it if 250watts psu can work with the following.

Intel i920 consumes (130 watts)
Intel i5 750 / i7 860 (95 watts)
Plus you will need GPU card (x watts )

Remember to get the best power consumption you need to enable EIST and CE1 in the BIOS and in Windows set your performance mode to balanced.

I suggest you read the following article as well:

How Many Watts Do We Need?
Related resources
September 19, 2009 9:59:21 PM

Thanks ibnsina. The power consumption tests in xbitlabs seems to be pretty informative. I've concluded that i7 920 + GeForce 260 system could be marginally fitted into 250-300W constraint as long as the GPU is idle. i5 750 should be use about 50W less, and there are less power hungrey GPU's out there. So sub-250W i5 750 system may be possible as long as the GPU is idle.

How much of the power is being drained off the 12V rail ? Are all of the CPU+Mobo+GPU going on th 12V rail ?
a c 144 ) Power supply
a c 172 à CPUs
September 20, 2009 8:17:40 AM

But an idle GPU is useless. A GTX260 will pull about 10 - 11 amps at 12 volts under load.

A motherboard by itself uses very little 12 volt power. Most of the power is used by the GPU and CPU and that's all off the 12 volt rails.

Memory is powered from the 3.3 volt output. I estimate 12 to 15 watts with 4 GB of DDR3 RAM.

Why the need to power this with a 250 watt PSU? I vote with Johnny. I do not think that you can reliably power a P55 systems with a 250 watt PSU.
September 21, 2009 10:34:53 PM

I need to use a 250W psu because it's going to be a DC-DC psu. I could find a similar 360W psu, but it only has 15 amps for the 12V rail. Guess I'll have to find a better psu.
a b ) Power supply
a b à CPUs
September 21, 2009 11:12:57 PM

Try looking at this article at x-bit labs, it breaks down power usage by component and is probably the article that jonnylucky referred to. It may help you figure out what you can use. The i5 750 would be a better choice then the i7 920.
I'd say if you used a low powered graphic card like the HD4650 and didn't overclock you could use the 250w power supply.
September 22, 2009 4:38:23 PM

What the main use of this system?
September 27, 2009 5:43:36 PM

If you don't need ultimate performance, Wait 6 months for Clarkdale - use the integrated graphics instead of a GPU - you'll need a P57 motherboard to support the integrated graphics, but 250 watts should then be no problem according to pcper:
"Even when pushing a four-thread run of CineBench 10, the Clarkdale system used about 70 watts of power"

"looking at PCMark Vantage, we find that the Clarkdale processor will offer about 43% better performance than your standard Core 2 Duo CPU available today."
September 27, 2009 5:48:20 PM

Actually, may not have to wait quite six months - Clarkdale still listed as due Q4 2009 - call it January to be safe.