2 Port Native PCI Express RS232 Serial Adapter Card with 16550 UART. 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 2000/XP/2003/Vista?/Windows 7/Server 2008 R2 (32 and 64 bit), Linux Kernel 2.6.11 and up, and MAC OS 10.4 and above. Plus, the serial card includes an optional half-height/low profile bracket that allows the card to be installed in any PCI Express slot, regardless of the size of the computer case. This product is a replacement for our PEX2S552 card. Backed by a StarTech.com Lifetime warranty and free lifetime technical support.