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Overclocking

The GeForce 8800 series has a sophisticated GPU frequency distribution. The main GPU domain can change its frequency with a variable step of 9, 18 or 27MHz, but the shader processor domain can change its frequency with a step of 54MHz only. The problem is that many overclocking programs can work with the main domain frequency only. In the standard GeForce 8800 GTX the frequency ratio is 1 to ~2.34, but pre-overclocked versions of the card may have a different ratio and their frequencies are going to change in a different way at overclocking. Fortunately, some overclocking tools, e.g. the latest version of RivaTuner, can report the real frequencies of the GPU domains to make the process of overclocking easier.

There is also a simple formula to calculate the frequency of the GeForce 8800’s shader processors during overclocking with a high enough precision:

OC shader clk = Default shader clk / Default core clk * OC core clk,

where OC shader clk is the (approximate) resulting frequency, Default shader clk is the initial shader processor frequency, Default core clk is the initial core frequency, and OC core clk is the frequency of the overclocked core.

Basing on this information and on the frequency monitoring data reported by RivaTuner, we attempted to overclock the graphics cards included into this review. Here are the results:

The ASUS has the best result in this test, which is remarkable as it does not have 1ns memory as the cards from OCZ and XFX have. The OCZ version has a lower memory frequency than the leader, probably due to the lower voltage of Samsung’s QE series chips. The memory chips of the XFX GeForce 8800 GTX XXX Edition are not much better at overclocking, either. Coming with a pre-overclocked main domain, this card has the smallest growth of the shader processor frequency as well. The XFX may be experimented with further by modifying it and updating its BIOS with a different value of the shader processor frequency – the card may show better overclockability then. The Foxconn FV-N88XMAD2-ON looks worse than the products from ASUS and OCZ, but its shader block frequency is higher than that of the XFX GeForce 8800 GTX XXX Edition, which may be more valuable in some cases than a higher main domain frequency.

These results should not be viewed as a direct recommendation to purchase the winner as having the highest overclocking potential. Your overclocking success depends largely on the abilities of the particular sample of the graphics card, besides a lot of other factors.

 
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