Computers were designed as general purpose machines with the ability to do anything in the digital world that one can imagine. The standard configuration of a machine may not suit the mind of a creator or artist, so they'll add something to it. Their are many different types of boards available and they can fit into different types of slots. The type of slot dictates how many things work inside of a machine. The most common features are integrated onto a computer's motherboard but they are addressed virtually as if the functionality were an expansion card.