PCIe has gone through multiple revisions since its inception. But the different revisions all use the same physical connections, and those connections can come in four primary sizes: x1, x4, x8, and x16, also but rarely x32.

The different physical sizes allow for different numbers of simultaneous data pin connections to the motherboard: the larger the port, the more maximum connections, colloquially known as lanes, on the card and the port. Different revisions of the PCI-E standard allow for different speeds on each lane.