PCI and PCI-X are not directly compatible, and you’d be forgiven for thinking that means you’re out of luck if you need to use a PCI-X card in a machine that only has basic PCI slots.

A device that adds wireless connectivity to a laptop or desktop computer ... cards that plug into an empty slot on the motherboard. See PCI and PCI Express. Cellular wireless adapters, also ...

the modem may also be available on a PCI or PCI Express (PCIe) card that plugs into an empty slot on the motherboard. For older laptops, modems may be available for ExpressCard or PC Card/CardBus ...