The pex2s553b 2 port pci express serial card w breakout cable lets you add two rs232 serial ports using a single pcie expansion slot with the included break out cable you can easily add two ports to a single low profile slot the pcie serial card features a native single chip design that provides optimum reliability and speed reducing the cpu load by up to 48 over conventional bridge chip serial cards a cost effective solution for connecting legacy serial devices to pcie enabled computers