PCI Express (PCIe) is an implementation of the PCI computer bus using existing PCI programming concepts based on a completely different and much faster serial physical-layer communications protocol. PCIe transfers data at 250 MiB/s per channel for up to 16 channels to achieve a transfer rate of 4 GiB/s.
The PCIe physical layer consists of a network of serial interconnects much like twisted pair Ethernet. A single hub with many pins on the mainboard allows all kinds of switching and parallelism. As clock rates increase, synchronization of parallel connections is hindered by timing skew. PCIe exemplifies a general trend away from parallel buses to serial interconnects.
Based on the existing PCI system, cards and systems can be converted to PCIe by changing the physical layer and adapting to PCI Express without any change in software. Higher speeds on PCI Express displace most existing internal buses, including AGP and PCI.
PCIe is the major new PC backplane standard, designed to be transparent to software developers, with the enhanced performance required for today's WLAN applications.