With PCI Express, data is sent serially through pairs of transmit and receive connections called lanes, which give data the ability transfer at 250 MB/s per direction. Multiple lanes can be grouped together into x1 (“by-one”), x2, x4, x8, x12, x16, and x32 links to increase bandwidth to the slot. For example, a x16 slot would have bandwidth of 4 GB/s per direction (250 MB/s * 16).
Figure 1. Various PCI Express connectors
Though different lane widths correspond to different physical slot sizes in PCI Express slots and connections do not differ physically based on the lane width of the link.