While most 64 - bit PCI - X cards are universal .
Are backward compatible with common 32 - bit 5 V PCI slots , PCI - X slots are 3.3 V and will not accept 5 V - only PCI cards .
While most 64 - bit PCI - X cards are universal and are backward compatible with common 32 - bit 5 V PCI slots , PCI - X slots are 3.3 V and will not accept 5 V - only PCI cards .