Graphics processing unit
The first attempts in Multi-GPU Systems were done by now defunct company 3Dfx in the late 1990s, which was bought by Nvidia later. Their Voodoo video cards, which were 3D only accelerators, could be hooked up to a second Voodoo video card to gain more performance. This was called SLi. Theoretically the performance would double, practically it increased far less, depending on the video game. Later, 3Dfx built even four GPUs on one unreleased video card.