What determines the number of PCI slots on a motherboard?
Computer Doctor: The number of PCI slots on a motherboard is determined by the chipset that the motherboard uses. For example, the Intel 440BX chipset http://developer.intel.com/design/chipsets/440bx supports a maxiumum of 5 PCI slots, while the 815E chipset http://developer.intel.com/design/chipsets/815e supports up to 6. If you download the datasheet for any chipset (from the chipset manufacturer), it should tell you the maximum number of PCI slots supported.