Closer Look at ASUS P5N-D Mainboard
Well, it is time for us to take a closer look at ASUS P5N-D mainboard. We will start with its official specifications:
If we compare these specs with the official specifications for Nvidia nForce 750i SLI chipset, we will see that ASUS laid out only one Parallel ATA connector of two supported by the chipset, which means we can only connect two devices of four possible. However, it is more than enough for today’s needs and many manufacturers out there do the same thing. Even Nvidia nForce 650i SLI based mainboards often had only one Parallel ATA connector.
There is another difference that seem pretty interesting to me, though. According to the official specifications of the Nvidia nForce 750i SLI chipset, ASUS P5N-D mainboard supports PCI Express 2.0 x16 mode for a single graphics card. As for two graphics cards working in an SLI configuration, they put it in a pretty strange way: “hardware ready for x16, x16”. What did ASUS actually mean? We all know that NVIDIA nForce 750i SLI based mainboard can formally work only as PCI Express 2.0 x8 + PCI Express 2.0 x8. Did they imply that the bandwidth of PCI Express 2.0 x8 equals that of PCI Express 1.0 x16? Of they are driving at the fact that there may appear an enhanced nForce 750i SLI supporting PCI Express 2.0 x16 + PCI Express 2.0 x16? Or maybe they were trying to say that NVIDIA nForce 200 bridge-chip supports PCI Express 2.0 x16 + PCI Express 2.0 x16 mode and the limitations are only made in the drivers, but not in the actual hardware?
The last version seems to me the most probable. The North Bridge of NVIDIA nForce 680i SLI chipset provided only 16 PCI Express lanes. The South Bridge added another 16 lanes necessary for PCI Express x16 + PCI Express x16 mode implementation. When they modified the chipset into NVIDIA nForce 780i SLI, 16 PCI Express 1.0 lanes from the South Bridge got assigned only for the third graphics card. However, Nvidia nForce 200 chip turned 16 PCI Express 1.0 lanes from the North Bridge into 32 PCI Express 2.0 lanes to be distributed between two PCI Express 2.0 x16 slots. So, why not do the same thing again with NVIDIA nForce 750i SLI chipset? It should be technically possible, but Nvidia has to clearly distinguish between the top 780i SLI chipset and its younger brother 750i SLI.
Of course, the question is how NVIDIA nForce 200 communicates with the? What interface it uses and at what speed? On the outside there are two PCI Express 2.0 x8 slots by NVIDIA nForce 750i SLI and two PCI Express 2.0 x16 slots by NVIDIA nForce 780i SLI. And what is inside? Could it really be PCI Express 1.0 x16, PCI Express 2.0 x1 or even PCI Express 1.0 x1? In this case, the current implementation of PCI Express 2.0 in NVIDIA nForce 750i SLI and NVIDIA nForce 780i SLI seems to be just a formality and it should be fairly easy to expand the functionality of nForce 750i SLI to supporting PCI Express 2.0 x16 + PCI Express 2.0 x16. In the meanwhile the owners of NVIDIA nForce 750i SLI based mainboards can only be certain about PCI Express 2.0 x8 + PCI Express 2.0 x8 support.
Well, let’s put all suppositions and guesses aside and discuss the ASUS P5N-D mainboard in detail.