This article is a continuation of my ongoing investigation of bottlenecking in video cards. The crux of it is to individually underclock the various clock speeds of a video card to see which has the biggest performance impact. Here are the past articles I’ve written on the same subject:
From the 8xxx series onwards it was possible to control core, shader and memory clocks on nVidia’s cards. With the 4xx series that has changed, and now the shader clock controls all non-memory clocks. More specifically, the core clock is always half of the shader clock.
Since there’s no real limit to how far we can underclock, I’ve chosen a nice round figure of 20%. I’ll individually underclock the shader and memory (leaving the other at stock) to see which has the most performance impact. This equates to a 972 MHz shader clock and a 1339 MHz memory clock.
The tests will be done on a single GTX470, and this card just happens to have about 16% less memory bandwidth than a GTX285, but has more pixel fillrate and shader performance. In light of this, it’ll be interesting to see whether the card is castrated by the reduced bandwidth.
1920×1200 will be used with both 2xAA and 4xAA, because these are quite realistic settings for someone gaming on a single GTX470.