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NVIDIA nForce 780i SLI
by Marc Prieur
Published on February 8, 2008

Logo NvidiaWhile NVIDIA rapidly dominated the chipset market for the AMD platform successively edging out VIA due with the evolution of its nForce since 2001, it’s a different story for the Intel platform. Here it should be pointed out that a bigger adversary is involved although this hasn’t stopped NVIDIA from persevering and with good reason of course. The creator of the GeForce thus comes back with a new high end chipset, the nForce 780i SLI, which replaces an aging nForce 680i SLI launched at the end of 2006.
A last minute delay
Initially, the nForce 780i SLI should have been launched at the beginning of November before it was delayed a month and a half. In fact, behind the delay there was a hidden compatibility problem with the Yorkfield, in other words, the 45nm version of the Intel quad core processor, which necessitated a redesign of motherboards.
Note that the nForce 680i SLI is also affected by the same problem although some manufacturers did specify its Yorkfield compatibility in the past. If EVGA, for example, adeptly resolved this situation by offering to exchange the nForce 680 for the nForce 780 and 80 €, this was unfortunately an isolated case.
An nForce 690i SLI ?

The main advantage of the nForce 780i SLI is in terms of PCI-Express which is now in its 2.0 version. You may recall, this now means attaining a data speed of 500 MB /s on each PCI-Express lane versus 250 MB /s for the first version.

This support however is a bit particular because it is done via the addition of a third chip, the nForce 200, to the already present SPP (northbridge) and MCP (southbridge). Connected in PCI-Express to the SPP, the new chip allows managing 32 PCI-Express 2.0 lanes which can be attributed to 2 to 4 graphic ports. In total, the bandwidth available between the nForce 200 and graphic cards is 16 GB /s. On the other hand, this figure is only 7.2 GB /s between the nForce 200 and the SPP as it is interfaced with the latter via 16 PCI-Express 1.0 lanes that are boosted 80% compared to their normal speed.

This doubling of the number of PCI Express lanes on the SPP level enables NVIDIA to offer a triple SLI solution with the nForce 780i which uses 3 ports cabled in x16, one of which is relayed to the MCP. On the 680i, the third port was in x8.
While NVIDIA had to rely on a new chip for PCI Express, this is actually because the SPP and MCP aren’t too different from the ones used on the nForce 680/650i. While there is Yorkfield compatibility due to a modification on the motherboard, at the current time we are still officially limited to FSB1333. This is when Intel will release the QX9770 in January which uses a FSB1600. In terms of memory, there is DDR2, still up to DDR2-1200, where Intel also offers DDR3 on the X38 (however note that DDR3 is actually of very limited interest at this time).

The southbridge remains the same and thus offers two Gigabit Ethernet ports which can be combined via DualNet technology as well as six SATA ports configurable in RAID 0, 1, 0+1 or 5.

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In practice, PCI Express 2.0  

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