Video Memory is not Reported Correctly on 64-bit OS
On Windows7 (64-bit) or Windows Vista (64-bit)-based computers that use a graphics adapter with 4 gigabytes (GB) or more of video memory, different user interfaces will report the memory information incorrectly.
For example, the DirectX Diagnostic Tool might show an “Approx. Total Memory” of 1259 MB on a system with 8 GB of video memory.
This is not an NVIDIA issue, but is due to the fact that several Microsoft APIs represent the video memory using 32-bits instead of 64-bits. On systems with 4 GB or more of video memory, this results in incorrect values reported to the UI or other applications.