Clock Frequencies and Overclocking

The special feature of the G70 processor we mentioned at the beginning of the review is the frequencies this chip is clocked at. It’s not a mistake to use the plural form of the word frequency here: different subunits of this GPU do work at different frequencies! The main frequency of 430MHz is for the pixel processors and raster operators (ROPs) whereas the vertex processors work at 470MHz (we’re talking about the 3D mode; in 2D applications all subunits of the processor are clocked at 275MHz).

We must make a small digression from the topic here. As our theoretical investigation revealed (for details see our article called NVIDIA GeForce 7800 GTX: New Architecture Exposed), the geometrical performance of the G70 GPU roughly equals that of the RADEON X850 XT Platinum Edition. The latter works at 540MHz, but has only six vertex processors against the G70’s eight. So it seems like the efficiency of the vertex processors in the G70 chip isn’t as high as with the RADEON X850 and X800, and NVIDIA had to increase not only their number but also their frequency to get to the same level of performance.

As we already know, the higher frequencies and the increase in the complexity of the logics didn’t affect the power consumption and heat dissipation properties of the G70 much if we compare it with the NV40, so the increase of the frequency of some subunits of the chip is a clever solution. Besides that, this separate-clocking feature can theoretically be used to control the power consumption more flexibly. But let’s get back to the EVGA card.

The GPU of the e-GeForce 7800 GTX works at 450MHz which is higher than the reference card’s 430MHz. The memory works at the same frequency as on the reference sample, i.e. at 1200MHz. But what subunit of the chip does this 450MHz frequency refer to?

NVIDIA’s representatives officially confirmed the fact that different units of the G70 work at different frequencies, yet we decided to check this out using the RivaTuner utility. The current version of this program (version 15.6) proved to keep track of the frequency of the vertex processors. When the GeForce 7800 GTX graphics card was working at its default frequencies (430/1200MHz), RivaTuner reported 470MHz in 3D applications and the difference between the two frequencies of the GPU remained constant (40MHz) whatever we did to them. The e-GeForce 7800 GTX thus has higher GPU frequencies (450 and 490MHz).

There is an opinion that the G70 can only change the frequency of the pixel processors and the raster operators with a step of 27MHz (this opinion is based on the fact that the GeForce 7800 GTX uses 27MHz quartz to issue the clock signal, but the same quartz is used in the GeForce 6800 series, by the way) and the frequency of the vertex processors with a step of 13MHz. We decided to check this out in 3DMark05 since this application always yields repeatable benchmarking results. For more precision we performed each test two times.