This is roughly the same as a PCI-X 64-bit connection (at 133 MHz ... within each lane for full-duplex operation. Today, PCIe 4 is slowly becoming adopted as more and more systems are upgraded.

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.

PCIe superseded PCI and PCI-X. Unlike its PCI predecessor, which used a shared bus, PCI Express is a switched architecture of up to 32 independent, serial lanes (x1-x32) that transfer in parallel.