I think this description applies to a mpcie-sata controller, such as: https://www.startech.com/eu/Cards-Adapters/HDD-Controllers/SATA-Cards/2-Port-Mini-PCI-Express-Internal-SATA-II-Controller-Card~MPEXSATA22I or similar controllers.
There has already been some discussion on similar controllers. See: SATA controller on MiniPCIe