Editing Peripheral Component Interconnect (section)

===Card voltage and keying===
[[File:Intelpromtserverpcixadapter1000mta342.jpg|thumb|A PCI-X [[Gigabit Ethernet]] expansion card with both 5&nbsp;V and 3.3&nbsp;V support notches, side B toward the camera]]

Typical PCI cards have either one or two key notches, depending on their signaling voltage. Cards requiring 3.3&nbsp;volts have a notch 56.21&nbsp;mm from the card backplate; those requiring 5&nbsp;volts have a notch 104.41&nbsp;mm from the backplate. This allows cards to be fitted only into slots with a voltage they support. "Universal cards" accepting either voltage have both key notches.