The power supply part or VRM (Voltage Regulation Module) of Radeon HD 4850 / 4870 is under-sized and thus are not able to support the current needed by the GPU when FurMark / OCCT are running. The VRM is under-sized because it has been designed to match the TDP (Thermal Design Power) of RV770-based graphics boards. And this TDP can be see as the highest reasonable load a card can support. Reasonable… I like this word! For a sub 50$USD graphics card I can understand it and in that case a single flat shaded triangle would be enough but for a 200$US+ graphics card, I should have the right to draw some furry objects.
Then to protect Radeon HD 48xx graphics cards, AMD has added in Catalyst 8.8 in simple protection based on FurMark.exe name (at this moment, OCCT didn’t have a GPU stress test). Recently, from Catalyst 9.8, AMD has improved the detection of FurMark and OCCT by adding this time a more serious technique based on the ratio of texture to ALU instructions. Okay these software tricks work and protect the RV770-based cards but the hardware problem still exists.
That’s enough for AMD! For Cypress based cards, AMD has hard-wired the protection and has implemented a hardware solution to the VRM problem, by dedicating a very small portion of Cypress’s die to a monitoring chip. This chip monitors the VRM. If the chip detects a dangerous situation (overload), the chip will immediately throttle back the card by one PowerPlay level. Once the dangerous situation has disappeared, the card goes back to its performance level. In the case of FurMark or OCCT, this can continue to go back and forth as the VRMs permit.
With this hardware protection, the Radeon HD 5870 is fully protected against FurMark or OCCT. One consequence is that a software protection in the driver is not needed anymore and you can use your favourite stress test tool to torture your brand new Cypress-based graphics card.
This protection has another consequence: cards with cheap VRM will be more throttle back than cards with high quality VRM. This difference will impact the processing power of the card and should be visible in FurMark’s benchmark score.
For me, this is a very nice news my friends! Why? Because I won’t waste my time to find the hack to make FurMark running on RV770 video cards (even if this would have been cool). Previous generation of Radeon will be quickly forgotten…
In conclusion, tools like FurMark and OCCT have pointed out some hardware problems in graphics cards and these problems are now fixed by GPU makers (currently only AMD is concerned). And thanks to the communication skills of our favourite GPU makers, everything is clear now 😉