GeForce GTX 690 Vs. Titan: The Differences Are Subtle
When you put GeForce GTX 690 and Titan next to each other, the two cards look like they share a great many characteristics, aside from the obvious fan configurations. But because one board dissipates 300 W of power and the other is for a 250 W GPU, there are some differences between them that aren’t readily apparent.
Those subtleties are important to the story. As Andrew’s team sought to “beautify,” they had to be mindful of thermal performance, which suffers if you try to go overboard on the details that simply look nice. The good news was that its dual-GPU (code-named Gemini) configuration indeed fit within that 300 W ceiling. Just one generation prior, GeForce GTX 590 was a 365 W card, requiring a more pointed emphasis on effective cooling. GeForce GTX 690 gave Nvidia a little freedom to get artsy. The cooler is consequently smaller than it would have needed to be for 590.
Here’s an example of how 690 and Titan differ. If you look across the 690’s top surface, you can see the polycarbonate windows recessed slightly, giving the face a greater sense of depth. But the shorter GeForce GTX Titan card, with its 250 W GPU, doesn’t have the same cooling headroom. Its PCB window is flush with the aluminum arms. This allows an additional 4 mm or so on the fin stack, which Andrew says is worth as much as 10% performance from the cooler.
Another example: Nvidia actually designed a back plate to cover the PCB. In the end, the plate was removed because it negatively affected SLI performance. We all know that the PCI Express electromechanical specification is very exact, and there’s only so much room between graphics cards installed back to back. Now, if you look down the top of a GTX 690, the fan sits just a bit lower than the card’s surface. This is done for airflow. Even when two boards are next to each other, that gap is large enough for the top card to suck in the air it needs. Unfortunately, the extra height of a back plate impedes airflow, impacting thermals by anywhere from six to nine degrees, according to Andrew. Were it not for SLI, covering the back of the PCB would improve cooling. So now the engineers are looking for ways to either design a plate that’ll work in SLI or be end-user-removable.
In my reviews, I’ve also commented on the fact that Nvidia went with a magnesium alloy fan housing for GeForce GTX 690, and then ditched it for Titan, 780, and 770. My understanding was that this had something to do with cost. But Andrew told me there really wasn’t much difference between magnesium and aluminum—at least as far as the metals go. More significant was the manufacturing difficulty.
There were actually two GeForce GTX 690 designs, one from magnesium and the other aluminum. The magnesium was a little lighter, though apparently not noticeably so. Its biggest benefit had to do with feature size, and when you set a 690 down next to a Titan, the 690 is just a bit stronger and more prominent-looking. Getting the finish on 690 was a nightmare, though. At first, the goal was to achieve a brushed aluminum look, like what you see from a kitchen appliance. The problem was that putting the shroud’s edges up against a sanding wheel to get the desired effect totally killed the detail. Sharp edges and corners were ground right off.
Once it was determined that brushing wouldn’t work, the team started experimenting with painting, raw finishes, and finally plating. None of it looked the way they wanted. By accident, some previously-plated parts were run through again, yielding an interesting result. And in the end, three plating technologies were combined to yield the finish Nvidia shipped to retail. It actually resembles the oxidized patina finish that some metals acquire over time; the 690 in our lab shows a soft glow of frequently-handled metal, while our Titans perpetually remind us that they’re painted.
But the biggest issue was that manufacturing yields started off around 10%. That’s not the GPU, mind you. Just the coolers. Because they were going from raw magnesium to plating, with no brushing or sandblasting in between, all of the dents from the casting line showed through. Someone had to manually sort through everything coming off the line and pick out the pieces without those imperfections. Even then, if you look closely enough, it’s still possible to pick out tiny divots in the metal.
Nvidia eventually got yields of the 690’s cooler up in the 30-percent range. Nevertheless, it’s understandable that the company quickly switched to a different design. But Andrew is still looking to improve further for generations to come. He wants to build a fan with an integrated hub, for instance, so that when the blades spin, you don’t see the center wobbling at all. It’s the difference between buying a car with hubcaps and one with rims, he jokes.