Just unboxed an XFX Radeon R7990 and decided to try it out with lite.
First impression, the card is extremely sturdy and well-built. The shroud is all metal. The heatsink and fan setup appear adequate at first glance. The card also has a metal backplate, which we have not yet seen from AMD with this generation of cards. The card is very long, seems longer than a 6990, though I didn't have one handy for comparison.
I installed it in a mid-size ATX case with quiet fans. The case fans do not push very much air, as they are designed for silent operation rather than performance. The 7990 is the only GPU in this case. I had to remove some hard drive caddies to make it fit, because it's so long.
This system is running Ubuntu 12.04 desktop with Catalyst 13.4. Immediate problem: this card does not work with 13.4. Catalyst 13.4 reports that no supported devices are installed, and xorg defaults to the vesa driver.
It is now working with 13.6 beta. This driver reports itself as "13.101," I'm not sure why. But the card is now working. I can also see that this card comes out of the box clocked at 1000 Mhz, instead of the advertised 950 Mhz. I also noticed that the memory is well overclocked as well, running at 1500 Mhz instead of 1375 Mhz.
Running lite 0.15 with --force, GPU performance is exactly to be expected. Same speed as 2x 7970. However we have an immediate problem with heat.
Even though this is a reference design card, it dissipates heat like an OEM cooler. The fans vent the air inside the chassis, not out the back of the card. There is no airflow coming out the back of the card at all, it is all coming out of the top of the card. Since this case does not have very powerful fans, the fans are not able to exhaust all the hot air the GPUs are pushing into the case.
Running lite, temps were around 86C for the GPU driving the display, and 80C for the second GPU. However, when the benchmark got to MD4. the temp on both GPUs spiked up over 90C. The GPU driving the 1080p display got up to 95C before I killed it.
I set the clocks at what would be a normal stock clock for a 7970 (non-Ghz edition), which is 950/1375, and manually set the fans to 100%. It ran about 6C cooler for all the algorithms, until we got to MD4 again, which made it spike up to 92C.
I dropped the core down to 850 Mhz and benchmarked just MD4 for 300 seconds, and while it stayed around 86C for most of the run, by the end it had reached 90C.
I think that if this card were used in a chassis which had sufficient airflow, such as a server chassis or open-air system, then it would not be too much of a problem cooling these cards. But it seems the largest reason AMD is able to claim that these cards are so quiet is because it's relying on the chassis fans to cool the cards. So I would not advise one to use this card in a desktop chassis at all, unless your desktop is populated with Delta fans.
Next week I will have the opportunity to install multiple 7990s into a proper server chassis with powerful fans, and I will let you know how the 7990 fares under those conditions.
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