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. The multiport PCIe Serial Adapter includes both full and low-profile/half-height brackets for compatibility with standard and small form factor computers and is compatible with a broad range of operating systems including Windows 7/Server 2008 R2 2003/Vista/XP (32 and 64 bit) Linux Kernel 2.6.11 and up as well as MAC OS 10.5 and above. This product is a replacement for our PEX2S552B card. Backed by a StarTech.com lifetime warranty and free lifetime technical support.