Most of the processing done on a computer is done via the computer's central processing unit, or CPU. So in order to give the CPU a break and help it run more efficiently, a video card can be used to process the graphics portion of the processing load. Because most of today's programs are graphically oriented, the video card can help almost any program run more efficiently. However, the difference in performance is especially noticeable in image editing applications and 3D games.
Video cards, also called graphics accelerators, can speed up both 2D and 3D graphics rendering. Programs such as photo editors and Web browsers may benefit from 2D acceleration, while CAD design programs and video games will most likely benefit from the card's 3D acceleration. Some programs rely so heavily on the video card, that they will not run if a supported video card is not installed.
Most video cards support the OpenGL and DirectX libraries. These libraries include commands for manipulating graphics that programmers can include in their code. Some of these commands may include moving or rotating an object, morphing polygons, or casting light and creating shadows. By using standard OpenGL or DirectX functions, it makes it easier for developers to create graphically-oriented programs. Of course, it also makes it necessary for the computer to include a supported video card in order for the program to run.
Video cards are typically installed in either the PCI or AGP slots in the back of a computer. Most computers come with a video card installed in one of these slots, which means it can be upgraded at a later time.