satanboy
Psychonaut seven
By James Wang
When NVIDIA set out to build the Kepler GPU architecture more than four years ago, our primary focus was power efficiency. We found that processors were increasingly being limited by the amount of power they could consume and dissipate. The only way to improve performance was to be able to do more work with the same amount of power.
That was our focus with Kepler, and when the GeForce GTX 680 launched last month, reviewers praised not only its record-setting performance, but also its incredible power efficiency.
Bjorn3D, a website that has tested graphics cards since the Voodoo era, summed it up nicely when it said: "Not only is the Nvidia GeForce GTX 680 the fastest single GPU card, but it is also the most power efficient and quietest high-end flagship card we have ever tested here at Bjorn3D."
While power efficiency is important to high-performance graphics cards, it becomes critical when building dual-GPU graphics cards. Here, two GPUs must vie for a finite amount of power, cooling, and board space. And it is here that Kepler shines the most.
The new GeForce GTX 690 is NVIDIA's flagship graphics card. Powered by two Kepler GPUs, it’s both a record setter in 3D performance and incredibly power efficient. In fact, the GeForce GTX 690’s performance is almost identical to a pair of GeForce GTX 680s in SLI, but with significantly reduced power and noise.
Not content with delivering only raw performance, our engineers went a step further. From Ferrari's F12 Berlinetta to the B&W's Nautilus loudspeaker, the flagship of any product category is invariably as much about form as it is about function. With the GeForce GTX 690, our engineers and industrial designers set out to create a new visual aesthetic to express the raw, uncompromising power of a dual-GPU Kepler graphics card.
The industrial design of the GeForce GTX 690 is a direct reflection of what lies beneath the cover: two Kepler GPUs, tremendous graphics horsepower, and a product of exceptional longevity. Visually, the design draws parallels to an F1 engine block with its raw metal look and exposed fin stacks.
The card's front plate is composed of two different materials. The exterior frame is made of cast aluminum with trivalent chromium plating, giving the board a durable, matte finish. The central fan housing is created from injection molded magnesium alloy. Magnesium alloys are used throughout the automotive and aerospace industry (including the engines of the Bugatti Veyron and F-22 Raptor) for their light weight, heat dissipation, and acoustic dampening properties. To create the intricate geometries required for the fan housing, we used a form of injection molding called thixomolding, in which liquid magnesium alloy is injected into a mold. This allows us to create fine geometries and a tight, perfectly coupled fit.
Cooling and Acoustics
The overall experience of gaming on a high-performance graphics card is very much influenced by its heat and noise output. The ideal card is fast, but stays cool and quiet.
The GeForce GTX 690 is cooled via a pair of custom vapor chamber heat sinks. Unlike a traditional heat sink that uses conduction to move heat away from the GPU, a vapor chamber exploits the superior heat conducting characteristics of evaporation. Inside each vapor chamber is a small amount of purified water. As the GPU heats up, the water evaporates, carrying away heat in the process. Once the vapor reaches the top of the fin stack, it cools, condenses, and the process repeats itself. It's similar to a miniature form of water cooling but, because the liquid is entirely self contained, there's no need for tubing and no chance of leaks.
Channeling air through the heat sinks is a center-mounted axial fan. The smoother the airflow, the lower the noise output. Here, our engineers spent considerable effort optimizing the fin pitch and angle at which the air hits the fin stack. The area directly underneath the fan is carved with low-profile channels to encourage smooth airflow and all components under the fan are low-profile so they won’t cause turbulence or obstruct airflow. Our acoustic engineers also fine-tuned the fan's control software so changes in fan speed occur gradually rather than in discrete steps.
The sum total of these efforts is not only in lower noise output, but also a less-perceptible noise. By eliminating board clutter, high-frequency sounds are removed. When you listen to the fan alone, it's clean and smooth.
Performance
A dual-GPU graphics card is similar to two-way SLI condensed into a single graphics card. Historically, though, the dual-GPU card has always lagged behind its SLI counterpart in terms of performance. When two GPUs are brought onto the same card, their combined heat output outstrips the capacity of even the most capable cooler. As a result, clock speeds must be lowered. For example, in the Fermi generation, the fastest single-GPU graphics card had a graphics clock speed of 722 MHz and a memory data rate of 4008MHz. On the dual-GPU card, the graphics clock was 607 MHz and the memory data rate was 3212 MHz.
This is where Kepler's fanatical focus on power efficiency pays off most handsomely. The GPUs on the GeForce GTX 690 have a boost clock of 1019 MHz, just a hair (2.8%) shy of the GeForce GTX 680 at 1058 MHz. What's more, all other specs are identical; the number of cores, memory speed, and memory bandwidth per GPU are the same on both cards.
What this means is that the GeForce GTX 690 performs more or less just like a pair of GeForce GTX 680s in SLI; almost nothing was compromised in bringing two Kepler GPUs to the same board.
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