With a small utility program GPU-Z, you can know all information about your video card and GPU.
GPU-Z utility supports both Nvidia and ATI cards. It displays adapter, GPU and display information. This utility displays overclock, default clocks and 3D clocks (if available). It supports Windows 2000/ XP/ Vista. No installation is required. Just double click the utility, then it displays all information about your video card as shown below.