Star Tech.com 2S1P Native PCI Express Parallel Serial Combo Card with 16550 UART The PEX2S5531P 2S1P PCI Express Card turns a PCI Express slot into two RS232 (DB9) serial ports & one Parallel port. The adapter card features a native PCI Express single chip design that means that you can take advantage of full PCI Express capability providing enhanced speed & reliability while reducing the load applied to the CPU by as much as 48% over conventional serial cards which use a bridge chip design. Compatible with a broad range of operating systems including Windows® 2000/XP/2003/ Vista™/ Windows 7/ Server 2008 R2 (32 & 64-bit) Linux Kernel 2.6.11 & up & MAC OS 10.4 this 2 Port Serial 1 Port Parallel PCI-Express Card also features an optional low profile/half-height bracket that allows the card to be installed in virtually any computer case regardless of the case form factor..