14-07-2011, 02:46 PM
PCI Express is positioned as the industry's third-generation I/O technology. First generation was ISA, second generation being PCI, and the third generation, PCI Express. PCI Express is designed to be a general-purpose serial I/O interconnects that can be used in multiple market segments, including desktop, mobile, server, storage and embedded communications. PCI Express can be used as a peripheral device interconnects, a chip-to-chip interconnects, and a bridge to other interconnects like 1394b, USB2.0, and Ethernet. It can also be used in graphics chipsets for increased graphics bandwidth. PCI Express is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. PCI Express is intended to be used as a local bus only. The PCI Express multi-drop, parallel bus topology provides Host Bridge and several endpoints. This introduces a new element, the switch into the system which replaces the multi drop bus and is used to provide fan-out for the I/O bus. A PCI Express switch provides high performance I/O and can coexist in many platforms to support today’s lower bandwidth applications until a compelling need, such as a new form factor, causes a fully PCI Express platform. Due to it being based on the existing PCI system, cards and systems can be converted to PCI Express by changing the physical layer only – existing systems could be re-booted on PCI Express and never even know it. The higher speeds on PCI Express allow it to replace almost all existing internal buses, including AGP and PCI.