Modern PCs allow users to convert multiple Graphics Cards into a single graphics processing unit. If I have to be specific, you can have as many as four Graphics Cards installed on a PC. But be sure of one thing, this will require you to use CrossFire or SLI system. A bit of intro about them, CrossFire and SLI Systems are technologies used to connect multiple Graphics Cards. While CrossFire represents AMD's products, the SLI Systems works fine for NVIDIA Graphics Cards. Believe it or not but it is an increasingly popular norm among gamers to connect multiple Graphics Cards and make them work as a single unit for enhanced graphics performance.