Startechcom 4 port pci express pcie rs 232 serial adaptor card startechcom pex4s553b the startechcom pex4s553b 4 port pci express serial card lets you add 4x rs 232 serial ports using a single pcie expansion slot with an included 1 to 4 cable enabling you to add 4 serial ports to a single low profile slot the 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