Is a PCI slot better than a 16 bit slot?

PCI-X is backward compatible with most cards based on the PCI 2.x or later standard. Originally the PCI bus was a 5 volt bus. Later, in PCI Revision 2.x the PCI bus was a dual voltage interconnect. In 3.0 this was changed to 3.3 volt only. The PCI-X bus is not compatible with 5 volt cards. Most newer PCI cards will work in a PCI-X slot, however, they will limit the speed of the entire bus. For example a PCI 2.3 device running at 32-bit and 66 MHz in a PCI-X 133 bus will limit the total throughput of the bus to 266 MB/s. To get around this limitation, many motherboard have separate PCI-X channels, allowing for better backward compatibility, and higher total bandwidth. PCI-X is also designed to be more fault tolerant than PCI. For example, PCI-X has provisions to reinitialize or deactivate a faulty card before a total system failure occurs.