PCI replaced ISA as the standard bus type, and unlike ISA buses, enables dynamic configuration of a peripheral device. When a system is booted the PCI card's BIOS and the system BIOS interact and negotiate the resources that the PCI card needs. This enables the PCI bus to provide a detailed description of all the connected PCI.
PCI-Express is a new version of the PCI computer bus that uses existing PCI programming and communications standards. Based on a much faster serial communications, it is being supported primarily by Intel\r\nThe higher speeds reached by PCI-Express will allow it to ultimately replace almost all existing internal buses, including AGP and PCI.
PCI-X is an extension to the PCI interface developed by IBM, HP, and Compaq. The extension allows data to be transferred at increased rates (up to 1 GB per second using a 64-bit bus running at 133MHz). PCI-X peripherals are fully compatible with older PCI and vice-versa, but will not run faster than the chipset or peripheral allows.
AGP (Accelerated Graphics Port) is a high-speed point-to-point channel for attaching a single device to the computer's motherboard. Many classify AGP as a type of computer bus; even though AGP does not allow multiple devices to be connected. Some modern motherboards have multiple independent AGP slots built-in.