ASUS implemented an interesting design with its high-end
P7P55D Premium motherboard, that makes use of a PLX PEX8613 3-port/12-lane PCI-E 2.0 bridge chip across its PCI-E 1.1 x4 from the PCH to drive the Marvell 88SE9123 2-port SATA 6 Gbps controller to its full-potential. Apparently the company plans to provide SATA 6 Gbps support using essentially the same design, for all its Intel P55 series motherboards by means of an optional addon card. Much larger than the SATA 6 Gbps card from
ASRock, the card from ASUS uses the same basic design that involves PLX PEX8613 as a PCI-E x4 device. The card uses the same SATA 6 Gbps controller to provide 2 internal SATA ports. From the looks of it, the card has placeholders for two controllers, with the second (absent) NEC µPD720200 controller providing USB 3.0 ports. Perhaps a future revision makes use of it. Planned to be offered as an optional accessory, this card could make for a premium over the base models.
Source: Hexus.net