There is a very good article detailing a history of the video cards that revolutionized personal computers.
"When 3dfx released their first card in October of 1996, it hit the computer world like a right cross to the face. That card was called Voodoo. This new card held the door open for video game development, accelerating 3D graphics like nothing before. The Voodoo card performed its magic via a pass-through connection to the user's regular 2D video card - a practice known as piggy backing. A few months later a new card was introduced, the Voodoo Rush, which combined both 3D and 2D functions into one card. However, it ran significantly slower than the normal Voodoo. This, combined with driver issues, caused the Rush to be seen as a flop by the community."