NVIDIA has been touting quad-SLI for a while now. Before this month it was only available as part of very expensive pre-built systems using four massive 7900 GX2 PCBs (printed circuit board) in two motherboard slots.

NVIDIA again piggy backs one PCB on to another and connects them with a 48-lane PCI Express switch resulting in what looks like a two-cards-in-one PCI-Express 16x slot. The 7950 GX2 uses 2 x 7900 mobile GPUs with cores clocked at 500MHz and 2 x 512MB 256-bit GDDR3 RAM clocked at 600MHz. There are 16 (2 x 8) vertex shaders and 48 (2 x 24) pixel pipes. Such layout resembles two 7900 GTs with faster cores and more-but-slower memory. And with (cooler) mobile architecture. Also note that while 1GB of RAM may sound a lot, each GPU can only use its allocated 512MB at once.

Each GPU sports a small HSF array which provides a quiet but audible swooshing noise. We recommend buyers have a well ventilated case however, as only one of the fans vents out the case’s rear and we found it got very hot.

NVIDIA claims that the 7950 GX2 is it’s fastest card but our testing didn’t always agree. At 1600 x 1200 it did indeed manage 2fps more than a 7900 GTX with 52fps and was only beaten by the 53fps of the X1900 XTX. In Call of Duty 2 it scored 34fps — one behind a 7900 GTX. However, it dropped considerably running at 1280 x 1024.

When running two cards in SLI (effectively quad-SLI) we saw a whopping 63fps in Far Cry but a strange drop in performance with Call of Duty 2 — just 30fps. We put the discrepancies down to driver issues but this will be a constant problem as the scalability of SLI relies on driver optimisations. With a 7950 GX2 it’s likely you won’t see top performance for new games until NVIDIA releases a compatible driver.

The features are good. This is the first card to include a key-ROM for playing encrypted HD movies. But with a release price of $1099 we’re not convinced it’s much more than a gimmick. It is potentially NVIDIA’s fastest card, but it’s not yet and it’s unlikely to ever be much faster than a 7900 GTX. But the real killer is that ATI’s cards are already faster.