Our Indulgence

The 7900GT launched just about a month ago seems to be eyed by a lot of enthusiasts holding a mid-range budget. For these group of gamers and 3D lovers, squeezing every bit of performance and image quality out of their hardware seems to be a growing trend. Let's face it: Most of us work hard to pay for our PC/gaming hobby. We put in that extra few hours of work everyday or skip that juicy steak meal at the fancy restuarants so we can have a wallet big enough to sustain our hobby.

Naturally, we want to maximize our enjoyment of our new toys, whether through the pleasing visual effects in our favourtie games, or through the big numbers we churn out in benchmark scores so we can boast to our friends about it. That's when a lot of us start to overclock our hardware, change out to alternative cooling on them, voltage modify them, etc.... in which the process ends up becoming a large part of the enjoyment, and not just the end.

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The 7900GTs are based on the G71 cores, fabricated on the 90nm process.

As a result of this fine die process, the heat output reduces and the potential of the clock speed capability of the chip improves compared to chipsets of the 110nm of the very recent yester months. In short, the G71 core using relatively lower voltage and humbler cooling has the potential to reach clock speeds the older G70 core struggled to hit even with increased voltage and exotic and extravagant cooling. If you have been following our past articles on the G70s, you would have read that very exotic solutions had to be used to hit the 800MHz ballpark, such as dual stage compressor cooling, dry ice and liquid nitrogen. How well do these new cards overclock comparatively then? What is needed to hit this level of speed, since the 7900GT comes clocked around the same speed as the 7800GTX?

Unchaining the Beast

The card in the limelight in this particular article is the reference 7900GT we've gotten from NVIDIA for our review just a short while back. You can check out our experience maximizing performance with it in the review as well. 550MHz is not too bad at all with the thin copper cooler that most of these cards come factory fitted with. With my trusty multimeter, I found that these cards run at a signifcantly lower voltage than their 7900GTX counterparts. If you compare the cores between the GT and GTX, you can see that they are actually very similar, both G71s that wear a 24-pipe-lined shirt. Of course, we can presume they are speed-binned such that the better ones are used on the GTX. But this bodes well for the 7900GT owners as the potential is likely there. My initial hunch is that the 7900GT are actually supplied with lower voltages so that a very simple single slot cooling solution and a relatively modestly rated power supply can be employed for these cards. True enough, from my testings, improving the cooling for these cards alone do little to increase the clock speed capaibility since they are so starved of voltage. Hence, we did some voltage modificatrions to give these cores the juice they need. This step is quite a neccesity if one truly wants to unlock the potential of these cards. For the details, look into our article here.

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We started off overclocking the card with 1.5v on the core voltage. It got rather warm with the modest default cooler so I decided to switch to something with more mass to chew on.

It is a nice copper cooler for previous generation CPUs. With some cable ties, I easily secured it onto my card. For good airflow over the heatsink and the entire card, I put on a silent 120mm fan.

The card was eventually tested on the ASUS A8R32 MVP Deluxe motherboard, with a mildly overclocked FX60 at 2.8GHz.

Letting it loose

I used Powerstrip to overclock the 7900GT. There are few overclocking software supporting these new cards right now and powerstrip is one of them. To get above the Clock speed limit you have access to, simply double click the icons circled in red.

Then change the % value to 199. And you have a lot more MHz at your disposal.

At 1.5v and with just air-cooling on this card, it hit 745MHz and 915MHz on the Memory, totally artifact-free!

That's almost a 300MHz and 65% overclock! Do take note at over 700MHz, increasing the memory clock speed is more beneficial for performance than increasing the core speed as the card becomes memory bandwidth limited in many situations. So if you have to choose between the 2 areas to overclock, you'll know which area to pick.

From there we took the voltage to 1.6v and climbed another 35MHz on the core and 10MHz on the memory.

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Up until this point, I have not increased the Memory voltage yet. I went onto increase Memory voltage to 2.2v and GPU core voltage to 1.7v.

The card was flying at 800MHz on the core and 1063MHz on the memory!! That's about an 80% overclock, and it broke through 7,000 points in 3D Mark 06. A remarkable feat for a USD$ 330 (SGD$ 550) graphics card.

Temperature wise, you can see that my air-cooling setup keeps it cool at 40C idle and 45C load right after it comes out of 3D Mark benchmark. This is roughly similar at 1.5v to 1.7v and different core speeds. The heat the card produces is really not that much even at 1.7v, and my air-cooling setup is more than sufficient to keep the card running cool.

Your Cue

Power and heat output-wise, I measured with my Clamp AMP Meter and below are some rough numbers. These figures are indicative of the card's power consumption and heat output when running 3D Mark 06 at 1280x1024. Of course when you increase the image settings, the power and heat will be slightly higher.

 

How about some practical application of this jug of GPU power? Well, we could game stably at 785MHz core and 1020MHz Memory artifact-free the whole day. I checked out how this improved my gaming experience for 2 games, Quake 4 and FEAR.

That's a huge difference, from 50+ frames per second, our VR-Zone OC Edition bumped frame rates to 80+! A 50% increase in performance there! Didn't cost much as well.

Sure, you definitely need some basic electronic skills to bring this card up to this kind of speed, but if you think about it, it's a lot less skills and effort involved compared to yester months. Funny how these things catch up wih us, just a few months ago, multiple compressors and other exotic forms of cooling were needed to hit this kind of speed:

What was needed a few months back

Now you don't even need to go water-cooling:

These cards are one of the most overclockable cards on air if you do it right. It will be fun to put 2 of these MHz monsters in SLI. What I find attractive about these cards is how accessible these clock speeds are. You don't need watercooling for it, just good air-cooling. And the SevenTeam 480W power supply we used during testing is more than enough to keep the card stable. A pity the voltage mod is not as simple as a pencil stroke or a BIOS flash. Share your overclocking results with us here.

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