If you want to add expansion cards to your system, you need to know what type of bus interface you need.
This is important because 5V cards are not compatible with 3.3V PCI / PCI-X slots and vice versa.

If you look at the images below you can see that the 32-Bit and 64-Bit slot differ in length.
The red arrows indicates the position of the notch(es) in the slot. These notches make it impossible to insert a 3.3V card in a 5V slot.

On normal desktop motherboards you probably won't find a PCI-X slot, but you can find these slots on workstation and server motherboards.


      Typical 32-Bit PCI slots.




      Typical 64-Bit PCI-X slots.








PCI-e slots are common on both desktop and workstation/server motherboards.
There're four types of PCI-e slots (1x, 4x, 8x and 16x) and are backwards compatible with each other.
For example: You can use a 1x card in a 4x,8x and 16x slot. All the Axxon I/O cards on this site are PCI-e 1x cards so you can use it on all boards with a PCI-e slot.

      The four types of PCI-e slots