Cooling System Design, Overclocking and Acoustic Performance
Now let’s have a closer look at the cards’ cooling systems:
The cooling systems of the Radeon HD 6990 and GeForce GTX 590 do not differ much in design, consisting of two heatsinks on a metallic base and a PWM-controlled fan in between them. The AMD card uses a classic 80mm blower whereas Nvidia prefers a 100mm axial fan.
The GPUs of the Radeon HD 6990 are cooled one by one: the air flows from the rear heatsink to the front one and is then exhausted. So, we can suppose that the GPUs are going to differ in temperature but most of the hot air will be exhausted out of the system case. The heatsinks of the GeForce GTX 590 are cooled equally because the fan drives the air towards both heatsinks, leaving half of the hot air inside the system case. The GPUs are likely to have similar temperatures as the result.
There are differences in the design of the metallic bases of the heatsinks. On the AMD card both heatsinks are soldered to it into a single whole whereas on the Nvidia card these components are separate, which makes it easy to assemble and dismantle the graphics card and, probably, ensures lower temperatures.
The heatsinks are hardly higher than 15 millimeters and look rather toy-like:
I wonder why Nvidia couldn’t make them some 5 millimeters higher. Both cards feature an evaporation chamber as you can see in the photos. Some dense gray-colored thermal interface is applied to the GPUs. Two types of thermal pads can be found between the cooler's base and the power components and memory chips.
Now let’s check out how hot these graphics cards are. To put them under load I ran the benchmark from Aliens vs. Predator (2010) in six cycles with maximum graphics quality settings at 2560x1600 with 16x AF but without FSAA:
It is at these settings that the GPUs had their highest temperatures. Monitoring wasn’t easy because the cards were so very new, but I got some information with MSI Afterburner 2.1.0 (by A. Nikolaichuk aka Unwinder) and with GPU-Z version 0.5.1.
Here are the results:
Both cards are very hot, just as expected. The temperatures of the Radeon HD 6990’s GPUs differ by 10-12°C whereas the difference between the GPUs of the GeForce GTX 590 is only 2°C. On the whole, the GeForce GTX 590 is colder than the Radeon HD 6990 by 10-12°C. Besides, I could measure the fan speed of the Radeon HD 6990 to be as high as 4800 RPM at such load. Of course, this was unbearably noisy. The GeForce GTX 590's fan is loud, too, yet its maximum speed of 2800 RPM is somewhat more comfortable.
At the same time, if Radeon HD 6990 runs at 830 MHz GPU frequency, the maximum graphics card temperature will drop by 5-6°C and the maximum fan rotation speed will not exceed 3100 RPM, which is, in fact, also pretty loud.
Now I want to add a few words about overclocking. The Radeon HD 6990’s cooling was too inefficient to hope for good overclocking, so I could only speed its GPUs up to 910 MHz. The memory frequency could be lifted up from 5000 to 6000 MHz, though, which is very good for a dual-GPU graphics card. As for the GeForce GTX 590, my sample could be overclocked from its default 607/1215/3414 to 725/1450/3940 MHz.
That’s good but hardly impressive. The Nvidia card’s GPUs didn’t get hotter when overclocked but the fan speed increased from 2800 to 3430 RPM. The Radeon HD 6990 got 2-4°C hotter when overclocked and its blower got even louder.