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-   -   Memory bandwidth (http://www.nvnews.net/vbulletin/showthread.php?t=25228)

ecoffey 02-22-04 11:47 PM

Memory bandwidth
Besides trial and error, is there some way to find out/calculate what the maximum usable memory bandwidth is for onboard video?

Thunderbird 02-23-04 10:40 AM

In the case of onboard video the bandwith is limited by the speed of the memory on your motherboard. For example when it is 333MHz ddr the bandwith (I assume you use single ddr which is 64bit): 333MHz * 8 bytes = 2.7 GB/s. Note that you need to check at what frequency the memory is really running.

ecoffey 02-23-04 02:38 PM

But I'm guessing that you can't run in a screen mode that demands the full bandwidth from your RAM, since nothing else would be able to access RAM. I am running at 333MHz, but in dual-channel mode (is that a simple doubling of bandwidth for these calculations?). Around the best video mode I can get is 32BPP 1600x1200@85Hz, which I calculate takes (I think this is right) 4*1600*1200*85 = 0.61 GB/s. So assuming a simple doubling for dual-channel my total bandwidth is 2*333*8 = 5.3 GB/s so my best video mode uses just a little under 1/8 of the total bandwidth. Could it be that maximum bandwidth for the nVidia driver is calculated simply as 1/8 of your total memory bandwidth?

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