Power management features have been defined in both PCI and PCI Express (PCIe) specifications, which are managed and released by the PCI SIG. These features are implemented in various “states” for the PCI bus or PCIe links, as well as for the various devices on a PCI bus or in a PCIe-based system. Understanding these power management functions is crucial to optimizing system power consumption. This article will review the standard power-management features for PCI and PCIe devices, then look at new power-saving features deployed in the newest generation of PCIe switches, to help engineers with the “greening” of the electronics industry.