The GX2 Uncovered

I guess up to now you gotten a good idea on how the NVIDIA GeForce 7900 GX2 looks like and what it is capable off. But what can we find beneath all that which is covered by the heatsink? Well that is exactly what you will get to see now. We removed the heatsink of the GeForce 7900 GX2 to see which main components we could find. And indeed we unfolded the GX2 so that we could check both PCB's and their related electronic structure and components.

Once the screws where loose we could easily remove the heatsink and the full scale PCB saw the light. The PCB is quite different from what we have seen so far on any GeForce 7 series based graphics card. Most of the electronic components have been visible, but not the main once who make the difference. We also would like to point out that there is an extra interface connecting both PCB's. There are actually 2 connections, one for the SLI function and one for the PCI Express interface switch. This switch has 48-line internal bandwidth which is divided in a 16-line link for each GPU and a 16-lane link for the PCI Express slot.

The GeForce 7900 GX2 is powered by the G71 series line of graphics processors, with each PCB equipped with one G71 core. The G71 core used is physically the same chip as you will find back on the GeForce 7900 GTX video cards and features 24 pipelines. The NVIDIA G71 chip uses a 90nm manufacturing process for its high performance circuits and is actually an optimized die shrink from the previous G70 chip. The GeForce 7900 GX2 core works at 500MHz operation speed, actually a lot lower clocked then the GTX which is set at 650MHz. The only reason behind comes from the heat produced by the dual core construction of the GX2 video card.

There is a new chip on the card that NVIDIA developed that acts as a physical PCI Express bus splitter. It takes the single physical 16-line PCI Express slot that is fed to the card and splits it into two full 16-lane PCI Express connections; one to each GPU. This logic is then responsible for the merging of the data back into a single 16-lane connection when it goes back across the PCI Express bus. The two PCB's are connected under the SLI bridge connections with a custom interconnect that allows the two GPU's to function in SLI mode.

And lastly some details on the memory chips used on the GeForce 7900 GX2 which will give a total of 1GB per card, meaning 512MB frame buffer per GPU. NVIDIA has opted for the high performance Samsung memory chips which are rated at 1.4ns. These same memory chips can also be found on the GT variant and are specified for 1.4GHz. Once more these are down clocked to only 1.21GHz which leaves some remove for improvement, so some potential overclocking. These should easily go up to 1.5GHz and even higher.