Now then, power consumption. Two cores usually cause a frighteningly high power consumption, that's just not the case at all. The GeForce 7950 GX2 obviously requires a very stable 12-volt power source for best stability, reliability and most of all that uber-powered gaming experience of yours.
For a GeForce 7950 GX2 graphics card, NVIDIA recommends a 400 watt power supply with 27 ampere on the 12 volts rails. So NVIDIA is recommending nothing exceedingly dramatic in terms of Wattage for the power supply unit yet be aware as that's a lot of Amperage on the 12 volts rail.
And noooo! That does not mean the graphics card is sucking up 27 amps! That's related to your entire system. NVIDIA did not state how much power each GPU consumes, but slipped in a document I did find out that both cores when stressed will use up 143W in total (for both). So it's safe to assume that each core can roughly use up (give or take) 75 Watts of power.
Simple math my fellow Guru3D inhabitants. If one G71 500 Mhz clocked GPU requires 75 Watts then:
75 Watts : 12 Volts = 6.25A (per GPU) So if you have a PSU with dual 12 volts rails a dedicated 14 AMPS on one graphics rail that rail would be sufficient. But a single 12 volt rail ampage of 27 AMPS is recommended as other components feed of that 12 volt rail too.
What we always do with new graphics cards is we measure the wattage peak with the help of a wattage meter. Slight side note, you are looking at the overall usage of the entire PC. The meter is placed between the power connector and the PSU. So please understand that using a Wattage meter is not the most reliable way of measuring power consumption. You basically look at how much power the PSU is pulling from the wall socket in your house. So you need to look at the results as being an indication and not an exact science.
The methodology: we simply look at the peak Wattage during a 3DMark05 session to verify power consumption. The graphics card consumes roughly 150 Watts at peak during 3D gaming, this is also the reason why we see a 6-pin power connector on the card as that much power being drawn over the motherboard is simply not possible.
In 3DMark the PC shows a maximum peak of ~340 Watts and that's quite good. We also experimented with a Quad SLI configuration a little and measured the power consumption on that one also... get scared. ~420 Watts.
The GeForce 7950 GX2 1024MB (in Quad configuration) with the rest of the components in the PC used up to 419 Watts.
So I agree, you need 400W at the bare minimum as you want some spare wattage - 450W or better is definitely recommended. When you buy a new PSU then look at the packaging and check the Ampere rating on the 12 volt rail, it should be ~25 AMPS at minimum. There are some good SLI certified PSU's out there, these have dual 12 volts rails dedicated for the graphics card. We highly recommend them! In fact we have been testing quite a few of them (see here).
What would happen if your PSU can't cope with the load ?:
bad 3D performance, FPS can fluctuate
spontaneous resetting PC
freezes during gameplay
PSU overload can cause a shut down or even break down of the PSU
So many things can happen, the PSU is really important.
Temperature of the graphics card
Twice the fun is two times the power and power means heat. Two graphics cores are now pushing heat into your system. The coolers on both the cores are small and dispose heat well. Yet one downside, they do dump it inside your PC. And a LOT of heat is disposed in there.
At idle, normal operation (i.e. your desktop), expect roughly 45 Degrees C. At 100% graphics core utilization we measured a maximum 73 Degrees C peak temperature on each GPU core, which is actually becoming a standard. The cooling fan at 100% utilization does not make a lot of noise at all, in fact the HD is producing way more noise then the cooler on this card and that's very nice to observe.
We measure with a (ambient) room temperature of 21 Degrees C.
Again a lot of heat is dumped inside your PC which I'm not happy about as it'll warm up the (inside case) temperature of the PC and thus also other components as well.
Noise levels coming from the graphics card
When graphics cards produce a lot of heat that heat needs to be transported away from the hot core as fast as possible. Often you'll see massive active fan solutions that can indeed get rid of the heat, yet all the fans these days make the PC a noisy son of a gun. I'm doing a little try out today with noise monitoring, so basically the test we do is extremely subjective. We bought a certified dBA meter and will start measuring how many dBA originate from the PC. Why is this subjective you ask? Well, there is always noise in the background, from the streets, from the HD, PSU fan etc etc, so this is by a mile or two not a precise measurement. You could only achieve objective measurement in a sound test chamber.
The human hearing system has different sensitivities at different frequencies. This means that the perception of noise is not at all equal at every frequency. Noise with significant measured levels (in dB) at high or low frequencies will not be as annoying as it would be when its energy is concentrated in the middle frequencies. In other words, the measured noise levels in dB will not reflect the actual human perception of the loudness of the noise. That's why we measure the dBa level. A specific circuit is added to the sound level meter to correct its reading in regard to this concept. This reading is the noise level in dBA. The letter A is added to indicate the correction that was made in the measurement.
TYPICAL SOUND LEVELS
Jet takeoff (200 feet)
Shout (5 feet)
Heavy truck (50 feet)
Normal conversation (3 feet)
GeForce 7950 GX2 XXX
Bedroom at night
We startup a benchmark, we take the dBA meter, move away 75 CM and then aim the device at the active fan on the graphics card. We measure roughly 42-43 dBa, which is to be considered a quiet to moderate noise level coming from the PC. Again, this is a very subjective test. But for two fans spinning at high performance, it's not bad for sure.
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