I'm going to buy a relatively old socket 370 motherboard on eBay as well as an Nvidia 6200 video card. Do I need to make sure the motherboard's AGP slot can support the video card's AGP speed, or will a 4X AGP card in a 1X AGP slot (for example) just slow down?
If memory serves, the 9700 PRO is the most compatible card out there with decent performance. Because it was among the first AGP 8x cards, it is 8x, 4x, 2x, and even 1x compatible I think.
The first gen 9700pro was like this. ATI eventually redid the card, losing support for anything that wasn't 8x/4x.
To the OP, you can't put a 8x card in a 2x slot. The AGP cards and slots are notched so that you can't put the wrong card in the slot. (well, not without noticable effort...) If the card fits in the slot, it should work. Do your research on the ebay motherboard (and seller...) and find out what AGP card you need. Don't neglect the 9700pro either, its probably faster then that 6200.
I would first like to say that your not the first person to ask this question or a similar question about graphics card signaling voltage.
Most manufactures do not explain what the signaling voltage is they only put a little side note and leave you to figure out what it means on your own, while supplying no explaination, hense everyones confusion.
Quite frankly I answer this question so often that I have the answer pre-written so I can copy and paste the answer when someone asks it which is usually once a friggin day it seems, anyway heres your answer. I have included a chart and key map to help you better understand AGP Standards.
I ran across this little "fact" when I was researching my 9700pro. I can't find the information now. I even looked at 9700pro images on yahoo's image search,and they are all 8x/4x/2x. Thinking back, this might be just a rumor I heard on eBay. (thats where I bought the card.) It might have been something the seller was claiming to make his card more valuable. (look, my card is 8x/4x/2x and not just 8x/4x) After finishing my quick yahoo search, they do all appear to be 8x/4x/2x.
Its in my wifes machine. Perhaps one of the best cards ever made. The fact that several years after it was released it can still play games of today is amazing. (granted the res won't be the best, but it will still play.) It was my second ATI card, I used it to replace my broken 9600pro.
I tried to upgrade from Radeon 9700 to Gforce 7800 GS half a year ago, but the card refused to function properly on my motherboard for some very strange reason. I got to the screen which showed that Windows was loading up, but nothing happened after that. The motherboard has 1x/2x/4x/8x AGP slot, as stated in the manual, but for unknown reason dxdiag.exe and ATI drivers show that fast write is disabled and the card is running at 1x AGP. I believe Gforce 7800 GS didn't function properly because it is only 8x/4x AGP, whereas Radeon 9700 works fine even at 1x AGP.