DirectX Diagnostic or DxDiag shows wrong total memory
Running the Microsoft DirectX Diagnostic Tool may show the incorrect total memory under the Display tab for a video card, as you can see in the image below. In this example, an NVIDIA GeForce 9800GT with 512 MB of video memory is being reported as 3303 MB approx. total memory.
This measurement is only an approximation of the total memory the video card uses and includes the total video memory and shared system memory in the computer.