Gigabyte’s P55A-UD4P cuts costs by using the processor’s PCIe 2.0 connections to host its high-bandwidth controllers. Two of the primary graphics card’s 16 PCIe lanes supply its USB 3.0 and SATA 6.0 Gb/s controllers, and Gigabyte disables six more lanes to make the upper slot an effective x8 interface. The USB 3.0 and SATA 6.0 Gb/s controllers revert to the chipset’s 2.5 GT/s lanes whenever two graphics cards are installed, to preserve the x8 transfers each graphics card needs for optimal CrossFire or SLI performance.
Thus, users with a single graphics card must sacrifice half of its peak bandwidth to enable 5.0 Gb transfers to the USB 3.0 and SATA 6.0 Gb/s controllers, while those with two cards must live with 2.5 Gb/s bandwidth limits on USB 3.0 and SATA 6.0 Gb/s controllers. Neither of these sacrifices is huge or even noticeable on most of today’s hardware, yet anyone trying to future-proof their system could be left cold.