Power Consumption and Heat Dissipation

24 pixel pipelines and 302 million transistors?Such a complex graphics processor should consume huge amounts of power, but the NV40 was already so voracious that the GeForce 6800 Ultra required connection to two Molex outputs of the power supply and NVIDIA recommended 480W and higher power supplies for owners of such graphics cards. We learned later that the recommendation was due to the fact that cheaper power supplies of less wattage just could not maintain stability of the output voltages well enough. In fact, the GeForce 6800 Ultra had power consumption comparable to that of the ATI RADEON X800 XT Platinum Edition, consuming about 72 watts under load against the RADEON’s 63 watts.

So what about the appetite of the GeForce 7800 GTX? Does it need a more powerful power supply than the GeForce 6800 Ultra? It does not! By using the new, thinner tech process NVIDIA even managed to decrease the consumption. NVIDIA recommends a 350W and higher power supply capable of yielding 22 amperes on the +12V rail for a system with a single GeForce 7800 GTX. It means the GeForce 7800 GTX is more modest in terms of power consumption than the GeForce 6800 Ultra and you don’t have to change your power supply if it already complies with the above-mentioned requirements. Of course, a more expensive power supply will be necessary for a system with two GeForce 7800 GTX (500W and better, 30 amperes on the +12V rail), but such computers are top-end and you are sure to have some money for a high-quality PSU if you’ve already purchased two such cards and a SLI-ready mainboard.

At our labs we have a special testbed that can measure the power consumption of PCI Express graphics cards. It is a specially modded platform of the following configuration:

• Intel Pentium 4 560 CPU (3.60GHz, 1MB L1 cache)
• Intel Desktop Board D925XCV
• 2x512MB PC-4300 DDR2 SDRAM
• Samsung SpinPoint SP1213C hard disk drive (Serial ATA-150, 8MB buffer)
• Microsoft Windows XP Pro SP2, DirectX 9.0c

We measure power consumption not only on the external power line but also on the 12V and 3.3V lines of the PCI Express x16 slot. Thus we get detailed information about power consumption of modern graphics cards.

To load the graphics cards with work we launched the most complex of 3DMark05’s tests, that is the third one, and had it running in a loop in 1600x1200 resolution, with enabled 4x full-screen antialiasing and 16x anisotropic filtering. The results are quite interesting: the GeForce 7800 GTX with its 302 million transistors, 24 pixel pipelines and 430MHz frequency consumed 80.7 watts under that load, while the much simpler GeForce 6800 Ultra had a consumption of 77.3 watts. There’s less than 3 watts of difference! So, the 0.11-micron tech process really helped NVIDIA to keep the power consumption of the GeForce 7800 GTX on the same level with the previous-generation model. By the way, the RADEON X850 XT Platinum Edition has a result of 71.6 watts which is slightly less than the consumption of NVIDIA’s cards, but it consumed much less than the GeForces on the 12V line (31 watts against 39-40 watts) and more on the 3.3V line (5 watts against 2 watts). The power consumption on the external line was similar with all the graphics cards, being about 33-35 watts.

What’s interesting, NVIDIA mentions quite different numbers talking about the power consumption of the GeForce 7800 GTX ?100-110 watts. Why so? They just mean the so-called peak consumption ?it’s when all the transistors in the graphics processor are working simultaneously, which is of course a purely theoretical situation. It is impossible to create such a load in real-life applications. According to our data, NVIDIA’s new graphics processor boasts an excellent efficiency: with all its numerous transistors and pipelines and higher frequencies, it consumes about as much power as its predecessor and does not require a power supply with the wattage of a welder. We can’t but congratulate NVIDIA on such a success!

So, people who own a GeForce 6800 Ultra or GT may go for a GeForce 7800 GTX without worrying about the power supply ?the current one will do nicely. In the same way, extreme users who have a SLI configuration of two GeForce 6800 Ultra will also be able to use their older PSU with the new cards. If the GeForce 7800 GTX is going to be your first graphics card or if you currently use a GeForce 6600 GT or a RADEON X700 PRO, you should purchase a high-quality 350 or even 400W power supply. Avoid cheap PSUs from obscure manufacturers! Such devices may be assembled by a simplified design and may not maintain the necessary stability of the output voltages. Such units may damage your graphics card as well as other system components.