The purpose of adding an expansion card or board to a computer's motherboard is to add or expand some sort of functionality to the computer that it did not have before. Expansion cards are a way to upgrade a computer. Tower case desktop computers embrace the expansion card concept more than any other case type. "On-the-desk" case desktops tend to sport a few expansion slots and all-in-one systems have limited expansion slot support if at all. As of June 2013, current production computers include PCI Express and PCI expansion slots.