I haven't been able to find particularly useful information from a web search about this feature. The board (Intel 9 series CPUs, ASRock H310CM-HDV) lists the usual CPU C state support options such as C3/C6/C7 support (all enabled), but with this last option which says in the description will enable it across PCIe devices / RAM as well. It's disabled seemingly by default (a BIOS update to the latest release version disabled it after I briefly enabled it). Any ideas?