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Please note we are only using FurMark as a tool to show the overclocking problem that we encountered. However, the problem was first noticed when benchmarking the overclocked Radeon HD 5970 in long stressful benchmarks such as S.T.A.L.K.E.R Clear Sky. In such games the overclocked Radeon HD 5970 failed to provide strong performance gains and if we looped the tests several times the results often ended up being lower than before any overclocking took place and this was because the card would throttle down to 550MHz. AMD did make it clear that the Radeon HD 5970 does throttle down to avoid any damage when operating at high temperatures. However they also portrayed the Radeon HD 5970 as a stellar overclocker that could and would hit Radeon HD 5870 speeds. While this is true to a certain extent as the Radeon HD 5970 will reach Radeon HD 5870 frequencies, it will also throttle back after a few minutes in certain stressful games such as S.T.A.L.K.E.R. So this is not really a practical overclock then since the card will inevitably throttle back. While it won’t happen as fast as it did in Furmark it will happen and that is the point. The Radeon HD 5970 is still a great product and it is the world’s fastest single graphics card but it is not the overclocking behemoth that AMD made it out to be. At least not with the standard cooler which they say is rated up to 400w. The overclocking issues were first uncovered using FurMark, which is an excellent program for placing full load on both GPU’s while measuring temperatures and performance. For the purpose of this article we clocked both GPU’s at 875MHz, while leaving the GDDR5 memory at the default specification. In order to achieve this overclock the core voltage must be increased and therefore we were testing at 1.1625v.  With the overclock now in effect we ran the FurMark benchmark at 1680x1050, please note that we did increase the run time for the purpose of this test. With the core at 875MHz, the average frame rate was sitting at a fairly constant 115fps. However after just 40 seconds temperatures exceeded 100 degrees and shortly after this the Radeon HD 5970 overclocking problem presented itself.  In order to avoid cooking itself, the Radeon HD 5970 throttles both cores down, negating any positive performance impact the overclock is going to have. However rather than throttle the cores down just a little, or even to the default operating specification, it drops the frequency to just 550MHz, that’s a 24% under clock on each core.  This saw the average frame rate decrease from 115fps before the throttling, to well under 100fps. The screen shot below shows an average of just 94fps after 260 seconds, with the temperature leveling off at 89 degrees. Eventually the average was reduced to 90fps, which is a 22% drop in performance. What we found interesting was that when testing with FurMark, the Radeon HD 5970 would even back off the card when operating at the default specification of 725/1000MHz. In fact, the only way we were able to avoid the throttling issue was to reduce the core frequencies to 650MHz, at this frequency the throttling never took place. |
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