Eddyworker wrote on 2021-05-27, 11:35:

hello, it is the first time that I write in this forum. I have followed him for several years and have learned many things. I have a 6800gt a400 windfast on a winxp and win 98 dual system, it works fine on both. In windows 98 I use the 77.72 drivers, the latest version fails at more than 60hz. I use an acer vg270 monitor through a dual dvi-d hdmi adapter. In the nvidia control panel I see all the frequencies that the monitor carries but when I exceed 75hz the monitor stays at 62hz, nvidia shows me that it is at 144hz but the monitor control panel at 62hz and I also notice the frequency drop . This happens in any resolution. In windows xp does not exceed 75hz. I have tried creating custom resolutions with various programs and the image is corrupted. I have tried several nvidia cards and always have the same problem on all windows os, only the 1050 or newest works fine. However with an ati 9200 ddr it works fine at 1280x1024 120hz. What is the problem here? Is it the monitor or an nvidia limitation? I would appreciate your comments. Thanks

1280x1024@120Hz, is out of spec for single-link DVI, which tops off at 162MHz for the pixel clock, unless you are using some extremely reduced blanking and your monitor and video card tolerate it . You are lucky it works with that ATI Radeon 9200 whose integrated TMDS is probably being run above spec, possibly significantly so .

As for DVI equiped Nvidia cards, AFAICT, the integrated TMDS on the 6800 is limited to single-link and thus 162MHz pixel clock as well. If the card uses an external TMDS chip that supports DVI dual-link AND the DVI to HDMI adapter is an active one that supports both dual link DVI input and HDMI 1.3 or higher output (at greater than 162MHz), then it might work.

That said, even if your Nvidia card is only capable of single-link DVI, but you can't even get something that fits within the 162MHz constraint to work (1280x1024@80Hz, for example), you might well be hitting a driver/firmware limitation on the card .

See https://tomverbeure.github.io/video_timings_calculator to calculate pixel clicks .

Thanks for answering. Come to the same conclusion, a limitation of the graphics card frequency. But in the process of resolv the problem, I have discovered some interesting things. First this video of the master PhilsComputerLab https://www.youtube.com/watch?v=xz8L5IuccAY

The second the capabilities of the dvi vary depending on the generation of the graphic and the brand. According to what I have personally tested in a 1050 the maximum resolution in single link dvi is 1600x1200 144hz and in dual link it is 2560x1440 144hz without compression, 32bit color, rgb color format and dynamic range full. On a 2000 quadro it is 2560x1440 90hz. This using the hdmi 2.0 port of my monitor, if I use the standard hdmi it is much lower. On amd vega 56 it is 2560x1440 90hz and the rest of amd that I have tested is 1280x1024 120hz but they are much older.

The third is that under debian linux I have managed to get 2560x1440 60hz with the 6800 gt in single link. Which makes me think that it should be able to get 1280x1024 144hz without a problem.

It would be perfect for someone with an nvidia card and a high refresh rate monitor will tell us about their experiences.

There is definitely a margin between, what works according to specs and what you can get away with by essentially overclocking a card's TMDS .

I personally would not want to overdrive a valuable (prices are going up and supplies will never increase) legacy video card's TMDS much beyond its rating. I might be more adventurous if using a card with an external TMDS chip as that can be replaced if it fails .

Again, personally, if was going to try getting higher refresh rates out of a 6800GT, I would

a) want to be able to run them at monitor native resolution, as much as possible
b) get a 6800GT that supports dual-link DVI
c) get something like this https://www.amazon.com/Gefen-GTV-DVIDL-2-MDP- … r/dp/B01LZT2Z15 (not an endorsement) to convert to DVI DL to Displayport, and, if necessary, cascade an active Displayport to HDMI 2.0 adapter

This may not be cheap, but will not be running anything out of spec and will have a better chance of actually working within the constraints of Nvidia's drivers.

Thanks for your recommendations. I am looking for 1280x1024 144hz at least. Its perfect for win 98 games. I think I am not overclocking the video output chip, I have always used gft and auto mode. The 1050 in automatic mode reaches 2560x1440 144hz using only a 583mhz pixel clock, in cvt it reaches 809mhz and does not give image. Replicating the 1050 timing system that nvidia uses with my monitor is the key to reaching higher resolutions with other cards. But that is beyond my knowledge. If I come to a solution I will write it in this post.

This implies that Apple sold a 6800gt variant with two dual link dvi outputs for their 30” displays in 2004/5

https://www.mactechnews.de/news/article/Nvidi … ich-128075.html