PCI Express

PCI Express, officially abbreviated as PCIe (and sometimes confused with PCI Extended, officially abbreviated as PCI-X), is a computer system bus/expansion card interface format. It was designed as a much faster interface to replace PCI, PCI-X, and AGP interfaces for computer expansion cards and graphics cards. The PCI Express (PCIe) physical connection (slot) is completely different to those of the older standard PCI slots or those for PCI Extended (PCI-X).

As with all computing standards, PCIe is a technology which receives further development and improvement. The current standard version in general use at time of writing is PCIe 1.1 however PCI-SIG announced the availability of the PCI Express Base 2.0 specification on 15 January 2007. PCIe 2.0 doubles the PCIe bus standard throughput or bandwidth from 2.5Gbps to 5Gbps. PCIe 2.0 is still compatible with PCIe 1.1 as a physical interface slot and from within software, so older cards will still be able to work in machines fitted with this new version. Further information on PCIe 2.0 is detailed below.

PCIe is a flexible hybrid serial-parallel interface format. That is, it uses multiple connections each of which individually transmit a single stream of data in parallel to one another. This type of interfacing is sometimes referred to as Channel bonding. PCIe 1.1 transfers data at 250 MB/s in each direction per lane. With a maximum of 32 lanes, PCIe allows for a total combined transfer rate of 8 GB/s in each direction. To put these figures into perspective, a single lane has nearly twice the data rate of normal PCI, a four lane slot has a comparable data rate to the fastest version of PCI-X 1.0, and an eight lane slot has a data rate comparable to the fastest version of AGP.

Unlike preceding PC expansion interface standards, PCIe is both full duplex and point to point. This means that while standard PCI-X (133mhz 64 bit) and PCIe x4 have the same data transfer rate, PCIe x4 will give better performance if multiple device pairs are communicating simultaneously or if communication within a single device pair is bidirectional.

While in development, PCI Express (PCIe) was referred to as Arapaho or 3GIO for 3rd Generation I/O.