I've had a few gpu problems and have gone from a XFX HD5870 to an ASUS Matrix EAH5870 2GD5.
Now, when I go into dxdiag, it says my approx video memory is 996 MB and is should say 2048 MB. So I uninstalled the ati 5xxx series driver, thinking that it might help if I were to install the driver from ASUS's site. After uninstalling the ati driver, I went to check what dxdiag might say, when no drivers were installed, and it was suddenly detecting 2048 MB, which is what the card should have. After installing the asus ati driver, dxdiag is back to showing only 996 MB yet again.
I wasn't sure if this really had any effect or not, as non of the games I played thus far, stuttered or lagged. However, then I launched Prototype. Prototype wont allow me to set my screen resolution to 1440x900 nor set AA any higher than x2, which was no problem with my previous HD5870 card. I read on activision's site, that Prototype wont give options for my desired resolution, if I have less than 1024 MB of video memory...
So this is where I'm beginning to think that dxdiag not showing the correct amount of video memory, might have some drawbacks after all.
My question to you guys: Is there any known way to correct this problem, where dxdiag doesn't detect the correct amount of video memory on your card?
I did a complete reinstall of windows 7 ultimate 64 bit and that didn't do the trick.
I'm sorry I don't have an answer, I am actually having the same problem. Did you ever get it to work? Because it also detects that my DDI ver: 10.1 instead of 11, right? I have tried a hotfix from windows' site the only thing to change was my 10.1 to 11, but I wanted it to show 2048MB and its showing 996MB now.
P.S I had problems with my OS as a whole after I installed the hotfix.
Gonna give a rather late reply here, didn't notice. Sadly no, I never found a fix for this issue, so I somewhat learned to live with it, since I don't see any apparent downsides to it... That didn't have a work around, game wise. WHen I play Prototype, I couldn't pick max settings and I thought this was the reason to it, not sure if it really was. Anyway, there was a workaround for that, although that left me with the windows cursor in the game...
Hope you have better luck than me and if you come across a fix, do let me know