PCI Express is a serial interface format, unlike PCI and PCI-X, which are parallel formats. Every device connected to a motherboard using PCI-E has its own dedicated point-to-point connection. Each of these connections is called a "lane" and is controlled by a switch. As a result of this architecture, connected devices don't have to share bandwidth passing through a single bus, as they would using PCI. This in turn enables more scalable performance, lower latency and higher data transfer rates. Condensing many parallel buses to one serial connection saves physical space on the back of servers and workstations, crucial where rack space is at a premium. PCI-E also allows hot plugging and hot swapping. 

 

Click here for Intel's video to learn more on PCIe GEN2 and high performance computing.