A couple of days ago news began to spread that (surprise!!) SLI support was coming to the world of Lynnfield and the P55 chipset.  Why this was a shock to so many people was confusing to me as motherboards had been advertised with “SLI Support” since Computex in June.  We saw examples from ASUS, MSI and Gigabyte as well as several other brands.

SANTA CLARA, CA—AUGUST 10, 2009—NVIDIA Corporation today announced that Intel Corporation, and the world’s other leading motherboard manufacturers, including ASUS, EVGA, Gigabyte, and MSI, have all licensed NVIDIA® SLI® technology for inclusion on their Intel® P55 Express Chipset-based motherboards designed for the upcoming Intel® Core™ i7 and i5 processor in the LGA1156 socket. As a result, customers who purchase a validated P55-based motherboard and Core i7 or Core i5 processor when available can equip their PCs with any combination of NVIDIA® GeForce® GPUs, including Quad SLI, for the ultimate visual computing experience.

There you have it.  SLI support will be permitted on P55 motherboards – but with a licensing fee paid to NVIDIA for every motherboard sold.  Keep in mind that AMD charges NO FEES for their CrossFire technology to motherboard vendors.  Just something to note if you care.

What is more interesting to discuss, that I haven’t seen mentioned much else where, is the status of 3-Way SLI on P55 platforms and the Lynnfield processor.  Because the x16 lanes of PCI Express 2.0 bandwidth coming from the processor itself can only be split into a pair of x8 PCIe connections, that would leave solutions using more than two cards out in the dark.  The PCIe x16 connection that comes from the P55 chipset itself, usually only configured as a x4 connection, would apparently cause a bit of a latency bump and performance hit if used as the “third” GPU slot in a system. 

The solution: another chipset from NVIDIA.  They are selling the BR-03 PCI Express bridge chip that takes a single x16 PCIe connection (in this case from the Lynnfield CPU) and splits it into either two full x16 connections or a single x16 connection and two x8 connections.  That would allow for three GPUs to communicate effectively and allow for 3-Way SLI configurations to exist.  Of course, this added chip will cost some more money and introduce some added complexity to the board design for any motherboard vendors that choose to implement it.

Perhaps more interesting, is that this BR-03 chip from NVIDIA will also be used to support CrossFireX configurations of more than two graphics cards.  According to this post from way back in March, the MSI G9P55-DC will do just that:

SLI coming to P55 chipset and Lynnfield CPU, but what about 3-Way? - Graphics Cards  1

So far we haven’t seen any other motherboards integrating this NVIDIA solution but we will keep our eyes out.  Either way, it looks like performance buffs will be satiated when it comes to SLI on Intel’s upcoming Lynnfield processor.