PCI Express, officially abbreviated as PCIe (and not to be confused with PCI-X, which stands for PCI Extended), is the latest interface to be found on PC motherboards for high performance cards such as the Spectrum M2i instrumentation cards. One of the advantages to PCIe is rapid appearance on PC motherboards and expected dominance over the next few years.
PCIe is based around serial links called lanes. With PCIe 1.1 (currently the most common version and used on Spectrum cards) each lane can theoretically carry 250 MBytes/second in each direction, however such a rate is not possible in reality because of transfer overheads. Spectrum PCIe cards are single lane, and typically provide speeds of about 130 MBytes/second, however this is still about 30% higher than the older standard PCI slot. Spectrum boards can fit PCIe slots with up to 16 lanes though only one is used. Note that for speed critical applications where three or less boards are in use, it is usually more advantageous to use PCI-X, the fast version of the PCI slot and a multi-bus PC controller motherboard.
PCI-SIG announced the availability of the PCI Express Base 2.0 specification on 15 January 2007. PCIe 2.0 doubles the theoretical data rate of each lane from 250 MB/s to 500 MB/s. A PCIe 2.0 PC slot is still compatible with PCIe 1.1 as a physical interface slot and from within software, so Spectrum cards are able to work in machines fitted with this new version, although there will be no performance advantage at this time.