Gentlemen, it looks like we can finally close 9600GT core clock mystery, which I’ve been brainstorming with my friends during the last 2 weeks. The mystery was not visible to public, however almost all reviewers noticed it during monitoring 9600GT clocks in realtime. Unfortunately, it was not exposed in majority of 9600 reviews, but TechPowerUp’s Zotac 9600 GT review is a good example of review which focused attention to it (please refer to “Wrong core clock?”): http://www.techpowerup.com/reviews/Zotac/GeForce_9600_GT_Amp_Edition/24.html Summarizing: NVIDIA insisted that they use 25MHz crystal for 9600GT’s core clock generation, which sounded a bit suspicious for us because it is simply not logical to use two different crystals on the same PCB and furthermore we couldn’t locate 25MHz crystal on the PCB. NVIDIA also refused to comment our questions about lack of 25MHz crystal on the PCB. However, yesterday I’ve found really interesting report in the forum, which pushed me in right direction and shed some light on the mystery. One of 9600GT owners (kudos to Gljukats @ overclockers.ru) reported that his 9600GT is really sensitive to PCI-E bus clock tweaking and even minor PCI-E clock increase increases 9600GT performance in 3D benchmarks (which are normally not limited by PCI-E bus bandwidth). This allows me to make the following conclusion: there is no fixed 25MHz reference clock and NVIDIA uses quarter of PCI-E bus clock (100MHz / 4 = 25MHz) as reference clock for core frequency generator. I’m almost 100% certain that my assumption is correct, however I still don’t have 9600GT installed and cannot verify it myself. Anyway, I hope that I’ll be able to do it really soon. So 9600GT owners should keep in mind that GPU clock is linked with PCI-E clock on these cards. So for example by overclocking the bus from 100MHz to 120MHz you also overclock your 9600 GT GPU by 20%. And the most tricky thing: you won’t be able to see clock frequency changes either in NV driver or in RivaTuner or any other software, because NVIDIA always uses fixed 25MHz crystal clock in the calculations.