PCI Express(pē-sē-ī ik-spres´) (n.) An I/O interconnect bus standard (which includes a protocol and a layered architecture) that expands on and doubles the data transfer rates of original PCI. PCI Express is a two-way, serial connection that carries data in packets along two pairs of point-to-point data lanes, compared to the single parallel data bus of traditional PCI that routes data at a set rate. Initial bit rates for PCI Express reach 2.5Gb/s per lane direction, which equate to data transfer rates of approximately 200MB/s. PCI Express was developed so that high-speed interconnects such as 1394b, USB 2.0, InfiniBand and Gigabit Ethernet would have an I/O architecture suitable for their transfer high speeds.
PCI Express, also known as 3GIO (for third-generation Input/Output) is compatible with existing PCI systems.