New Features and Some of the Same

A Fresh SPP, or Two

NVIDIA’s 790i introduction actually consists of two chipset offerings: the nForce 790i Ultra SLI and the nForce 790i SLI. The former uniquely accommodates 2,000 MHz DDR3 memory modules, whereas both solutions share the higher-speed FSB option, PCI Express 2.0, and the circuitry needed for 3-Way SLI.

Let’s start from the top of NVIDIA’s 790i block diagram and work our way down.



As mentioned, both 790i SPPs (system platform processors—the equivalent of a north bridge) are able to communication with Intel Core 2 Extreme, Quad, and Duo CPUs over a 1600 MHz front side bus. Where’s AMD’s processors incorporate integrated memory controllers, Intel’s do not. Thus, the 790i sports its own built-in controller circuitry. This is NVIDIA’s first attempt at DDR3 support, so it’s pretty amazing that we’re seeing up to 2000 MHz right off the bat.

The 790i Ultra SLI supports standard JEDEC modules at 1333 MHz, or higher memory frequencies through NVIDIA’s EPP (Enhanced Performance Profiles) 2.0 spec. Boards based on vanilla 790i SLI components officially top out at 1333 MHz. Naturally, you’re going to pay more for the Ultra, so it’s important to understand a few things about running those super-fast operating modes. First, at 2000 MHz, the timings of today’s modules are in the 9-9-9 range. Second, while 790i-based boards include four memory slots, you’ll only be able to use the second and fourth slots at high speeds. It’s a slot addressing thing, NVIDIA says. Any other configuration and your board won’t boot.

Fortunately, when you have the hardware set up properly, the EPP 2.0 spec makes it easy to get up and running with the right timings at 2000 MHz. In addition, you don’t have to use extreme voltages to coax those speeds from compliant modules. Our OCZ SLI-Ready kit was comfortable at 1.9v.

Owners of NVIDIA’s 780i will notice that this chipset doesn’t use the nForce 200 companion chip, which cobbled on PCI Express 2.0 support. The 790i offers 32 lanes of PCIe 2.0 natively, comparable to the other high-end chipset in LGA775-land, Intel’s own X48 Express. Those 32 lanes are divided between a pair of x16 slots.

“But doesn’t the 790i do 3-Way SLI?”

It does. The third x16 slot is derived from the 790i MCP (the Media and Communications Processor, which you know as a south bridge). Armed with 28 lanes of PCI Express 1.1 connectivity, NVIDIA’s 790i MCP lends 16 of them in the name of more graphics horsepower.

If you do plan on using 3-Way SLI with 8800 GTX or 8800 Ultra cards, populating that third x16 slot will cost you more than just PCI Express 2.0 support. The SPP’s 32 lanes benefit from two optimizations designed to improve the efficiency of SLI—PWShort and Broadcast. The first feature enables point-to-point communication between GPUs, freeing up memory bandwidth. The second, as its name suggests, broadcasts the same data to GPUs in parallel, rather than one at a time. Both capabilities are functions of the SPP, so you don’t get them from the third slot. Fortunately, there’s always the option of going Quad-SLI using a pair of GeForce 9800 GX2 cards. The 790i does support that configuration with SLI speed-ups enabled.

Communication between the 790i SPP and 790i MCP is facilitated through a HyperTransport link with plenty of throughput for the south bridge’s copious I/O. We’d suggest that Intel take notes, but the next ICH is already expected to alleviate the narrow DMI connection currently being used.

I Believe We’ve Met

Make your way down to the 790i SLI MCP and you should start seeing some similarities to past south bridge components. Six SATA ports, one parallel IDE channel, HD Audio, dual Gigabit Ethernet controllers, 10 USB ports. Yeah. It’s the same list of features found on the 780i MCP, the 680i, and the 590i. Specifically, the 790i SLI MCP is actually a 570 SLI MCP with a new name.

Not that we’re complaining. The aging I/O controller was actually ahead of its time back in 2006 and still compares favorably to Intel’s ICH9 and AMD’s SB600. The Intel ICH only offers six PCI Express lanes, while AMD relies on its north bridges for PCIe links (granted, the 790FX swings 42 lanes of PCI Express 2.0, so the match-up is a tad skewed).

From left to right, PS/2 connectivity, digital audio outputs, eSATA, FireWire and USB, 7.1-channel analog audio, Gigabit Ethernet, and more USB.

The 790i SLI MCP comes up a little short on USB connectivity versus Intel’s ICH and ties AMD’s SB600 with a maximum of 10. Then it beats out the ICH9 by including a single parallel ATA channel. However, AMD offers as many as two. The dual Gigabit controllers are certainly a nice touch versus Intel’s one Gb port and AMD’s reliance on third-party networking vendors. Finally, not only do you get six SATA 3 Gbps ports, but there’s also NVIDIA’s MediaShield technology. Software support for RAID 0, 1, 0+1, 10, and, uniquely, 5 give you plenty of performance- and data security-enhancing options.