Complex sentence: Connector on the host side accepts either one PCI Express SSD or up to two legacy SATA devices, by providing either PCI Express lanes or SATA 3.0 ports depending on the type of connected storage device.
Split into simpler sentences: Connector on the host side accepts either one PCI Express SSD, or up to two legacy SATA drives. The host connector is providing either PCI Express lanes or SATA 3.0 ports, depending on the type of connected storage device.