A PC Expansion Bus, as the term implies, is a bus that expands the Personal Computer's internal interface bus. The bus or buses that reside on the PC's Motherboard are the buses being expanded. Cable interfaces or Peripheral interfaces are not being referred to.

The common reference to a PC Expansion bus refers to expanding to, or adding functionality to the normal internal computer bus. So the term PC Expansion Bus refers to the additional expansion bus slot residing on the PC's Motherboard.

Most motherboards produced will contain Expansion slots, or connectors to accept additional cards to enhance the computers functionality. However, the type of expansion slot will vary depending on the age or function of the motherboard.

On an up-to-date motherboard the expansion bus offered will be PCI-Express. Depending  on the application the motherboard will have either 1 or 2 PCI Express slots for a video interface [PCIe x16], and 2 or 3 slots for other functions [PCI x1]. PCIe is another term for PCI Express, while the x1, or x16 refer to the number of lanes or bandwidth.

Computer motherboards produced in 2005 have a combination of PC Expansion buses, with 1 or 2 connector slots using PCIe for Video cards, and 2 to 4 slots for a PCI Boards. The PCI interface has been around for a number of years and has a larger base than PCIe. There are many PCI cards that have been developed to provide a number of functions, while low end PCIe cards are just now coming out [because the motherboards don't have PCIe 1x slots.]

Obsolete PC Expansion Buses include the ISA bus, the EISA Bus, and the VLB bus..

For a full list of computer buses refer to the Personal Computer Buses page, listed on the web site http://www.interfacebus.com/,