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Overclocking with Delta Modification

In our previous articles we wrote that the so-called delta modification (a reduction of the frequency of one of the GPU subunits to increase the frequency of other subunits on Nvidia’s new GeForce 7 series graphics cards) is a way to get a couple of extra frames per second in your favorite game.

Now I’m going to tell you what exactly and how can be changed and what practical gains it may give you.

First of all, you should know that all the GPU subunits work at the same frequency on new graphics cards, but it is the geometric subunit that becomes the main limiting factor at overclocking. By lowering its frequency in the BIOS relative to the other two subunits (raster operators and shader processors), it is possible to lift up the max frequency the GPU can work at.

We need a fresh version of the nvflash utility that recognizes your graphics card and the Nvidia BIOS Modifier, a utility to change the settings written into the BIOS of graphics cards based on Nvidia’s chips.

You copy nvflash on a boot diskette, reboot and save the original BIOS (type “nvflash –b filename.rom” into the command line).

To modify the delta, open the BIOS image with the Nvidia BIOS Modifier and select the desired negative delta (or positive if you want to make the GPU non-overclockable :)) on the Performance Table tab:

Save the modified BIOS on the diskette, reboot and type in “nvflash –f modified.rom -4 -5 -6”. That’s all! The optimal value of the delta must be found out by a cut-and-try method.

I set the delta at -85MHz for my Gainward Bliss 7600 GS 256 MB Golden Sample. This helped increase the frequency of the shader processors and raster operators to 838MHz. The vertex processors worked at 753MHz. This can be described with the formula 753/838/838 (geometric/shader/ROP)/816 (1632) MHz.

I benchmarked the graphics card in this mode to evaluate the performance gain from such a modification.

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