The pex2s553 pci express serial card lets you turn a pci express slot into 2 rs232 db9 serial ports based on a native single chip design no bridge chip this 2 port serial adapter card allows you to harness the full capability offered by pci express pcie and reducing the load applied to the cpu by as much as 48 over conventional serial cards the rs232 serial adapter card pex2s553 is compatible with a broad range of operating systems including windows 2000xp2003vistawindows 7s