The 3ware 9550SX PCI-X card is 3.3 V only, and doesn’t fit in a typical PCI slot. It’s not compatible ... is probably finding a PCI-X riser; PCI-Express stuff is far more common.
PCI Express (PCIe) was introduced in 2002 as "Third Generation I/O" (3GIO), and by the mid-2000s, motherboards had at least one PCIe slot for graphics. PCIe superseded PCI and PCI-X. Unlike its ...