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A software developer who is behind the famous RivaTuner utility for graphics cards’ tweaking said specifications of graphics cards powered by NVIDIA GeForce 6800 graphics processing units may be slightly changed by makers of actual add-in cards which results in lower geometry performance and also affect actual speed delivered by the product.

GeForce 6800 May Feature 5 or Less Vertex Processors

When NVIDIA initially unveiled its GeForce 6800-series lineup it was believed that the GeForce 6800 Ultra and GeForce 6800 graphics processors featured equal number of geometry processors amid different amount of pixel processors and clock-speed. Now it turns out that at least some GeForce 6800 graphics processors feature less geometry processors than more advanced “Ultra” and “GT” models.

“I have found the way to detect and enable/disable active vertex units on NV40 boards. The most surprising fact is that all 6800 non-Ultra graphics cards I have seen have at least one disabled vertex processor too, so just 5 or less of them are active instead of 6 in Ultra models,” Alexey Nikolaychuk, the author of RivaTuner, said in his blurb over Guru3D web-site.

The GeForce 6800 Ultra packs in 16 pixel pipelines and 6 vertex pipelines, the GeForce 6800 GT reportedly integrates the same amount of pixel and vertex processors. The GeForce 6800 sports 12 pixel pipes, but it is now unclear whether it has 5 or 6 geometry engines.

Leading graphics chip designers, such as NVIDIA Corp. and ATI Technologies, reserve ability to disable certain circuitry within graphics processors in case that logic works incorrectly. Previously ATI was renowned for disabling defective pixel pipelines in cut-down versions of its processors, now NVIDIA is seemingly able to deactivate both pixel and vertex processors. Sometimes such disabled circuitry inside graphics chips can be enabled via BIOS flash, software modification or hardware modding, however, in a number of cases this leads to incorrect rendering afterwards.

Graphics processors with deactivated pixel or vertex pipelines typically deliver lower performance compared to chips with fully-functional units.

“I would like to warn everybody going to buy non-Ultra 6800. We have already detected $350 OEM Leadtek [GeForce] 6800 graphics cards in Russia, which have 2 disabled quads and 2 disabled vertex processors,” Mr. Nikolaychuk added.

Clear Specifications Unknown, but Leadtek Sheds Some Light

Whereas the number of graphics cards powered by the GeForce 6800 graphics processing units with allegedly lower than expected geometry performance is unknown, actual specifications for the GeForce 6800-based graphics cards are also not officially declared.

Please click to enlarge

NVIDIA did not have clear list of specifications for different GeForce 6800 models on its web-site at press time. The majority of graphics card makers also do not reveal in-depth specs of the GeForce 6800 graphics cards they ship. The only maker that presents comprehensible list of GeForce 6800-series specifications is Leadtek. The table plainly states that the GeForce 6800 delivers lower geometry performance – 406 million vertexes against 600 and 525 million of more powerful chips – compared to the GeForce 6800 Ultra and GeForce 6800 GT models. The difference in geometry performance submitted by Leadtek is higher than the difference in clock-speeds between various models.

Clarification from X-bit Labs

Reference GeForce 6800 graphics card provided by NVIDIA Corp. and used by X-bit labs’ laboratory in Tallinn, Estonia, scored identical fps in Xbitmark vertex shader test against NVIDIA’s reference GeForce 6800 Ultra graphics card working at the same clock-speeds, indicating equal per MHz geometry performance of the 6800 model against the “Ultra” model.

Such results are unlikely to represent certain changes in vertex processors array and indicate lower number of such units within the chip. In case the majority GeForce 6800 come with 6 geometry engines, X-bit labs can reaffirm that the GeForce 6800 benchmark results available in our articles are correct and reflect speed of the majority actual graphics cards available on the market. Performance figures delivered by our articles should not be extrapolated on the GeForce 6800 flavours with 5 or less vertex pipelines.

It is unclear whether additional vertex processors can be enabled by reflashing a more advanced BIOS. Some pre-production BIOS versions caused inadequate results and behaviour on some GeForce 6800-based graphics cards.

Representatives for NVIDIA Corp. did not comment on the news-story on Sunday.


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