Startech com pex4s553 4 port native pci express rs232 serial adapter card startech com pex4s553 p the pex4s553 4 port native pci express rs232 serial adaptor card with 16550 uart from startech com lets you add 4 rs232 db9 serial ports using a single pci express expansion slot p p based on a single chip design this 4 port serial adaptor card allows you to harness the full capability offered by pci express pcie while reducing the load applied to the cpu by as much as 48 over conventi