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Comparing the competition
Today we've assembled the four chipsets you're most likely to find on enthusiast-oriented motherboards for Core 2 processors: the P965 Express and 975X Express chipsets from Intel, and the nForce4 SLI X16 and nForce 570 SLI from Nvidia. Here's a quick look at their north bridge chips' specifications.

975X Express P965 Express nForce4 SLI X16 SPP nForce 570 SLI SPP
Front-side bus 1066/800MHz 1066/800MHz 1066/800MH 1066/800MH
Memory controller DDR2-667 DDR2-800 DDR2-667 DDR2-667
PCI Express lanes 16 16 20 20
Multi-GPU support CrossFire CrossFire* SLI SLI
Chipset interconnect DMI DMI HyperTransport HyperTransport
Peak interconnect bandwidth 2GB/s 2GB/s 8GB/s 8GB/s

Interestingly enough, only the P965 has explicit support for DDR2-800 memory. The rest top out at DDR2-667. That hasn't stopped motherboard makers from building 975X, nForce4 SLI X16, and nForce 570 SLI boards with the necessary dividers to run their memory at 800MHz, though. We've even seen boards supporting memory speeds of 1066MHz.

Judging by the table of north bridge features above, Nvidia appears to have an edge when it comes to PCI Express lanes. Since some of these chipsets offer PCI-E lanes from their south bridge chips, though, that isn't the whole picture. The nForce chipsets are, however, the only ones with Nvidia's blessing to work with its SLI multi-GPU technology. The nForce4 SLI X16 even does so with a full 16 lanes of bandwidth to each graphics card. Multi-GPU graphics support on Intel chipsets is presently limited to ATI's CrossFire, which is only fully implemented on the 975X. ATI just announced support for CrossFire on P965 boards with its latest Catalyst 6.9 drivers, but only for Direct3D applications. OpenGL support should be added by year's end.

Chip-to-chip interconnect bandwidth is one area where the nForce chipsets have a definite advantage over their competition. HyperTransport serves up a cool 8GB/s of bandwidth between the nForce chips' north and south bridge components, while the P965 and 975X are limited to only 2GB/s via Intel's Direct Media Interface (DMI). DMI hasn't proven to be a bottleneck in the past, so Nvidia's advantage here may be theoretical at best.

By following the chipset interconnect, we find the 975X north bridge paired up with the ICH7R south bridge, the nForce SPPs matched with their respective MCPs, and the P965 paired with either the ICH8 or the ICH8R.

ICH7R ICH8 ICH8R nForce4 SLI X16 MCP nForce 570 SLI MCP
PCI Express lanes 6 6 6 20 0
Serial ATA ports 4 6 6 4 4
Peak SATA data rate 300MB/s 300MB/s 300MB/s 300MB/s 300MB/s
Native Command Queuing Y N Y Y Y
RAID 0/1 Y N Y Y Y
RAID 0+1/10 Y N Y Y Y
Matrix RAID Y N Y N N
ATA channels 1 0 0 2 2
Max audio channels 8 8 8 8 8
Audio standard HDA HDA HDA AC'97 HDA
Ethernet N N N 10/100/1000 10/100/1000
USB ports 8 10 10 10 8

Intel prefers PCI Express peripherals hanging off the south bridge, so like the ICH7 before it, the ICH8 features six PCI-E lanes. The nForce 570 SLI, meanwhile, consolidates all its PCI Express on the north bridge. Because it hangs secondary graphics cards off the south bridge, the nForce4 SLI X16 chipset has an additional 20 lanes of connectivity in its MCP. Given its feature set, we suspect that the nForce4 SLI X16 MCP is in fact an nForce4 SLI chip (familiar from so many Athlon 64 motherboards) that's been pressed into service as a south bridge chip.

Each of the chipsets supports 300MB/s Serial ATA transfer rates, but the ICH8 and ICH8R are the only ones to provide six SATA ports. (Interestingly, the nForce 570 SLI for AMD processors also sports six SATA ports, but its Intel cousin does not.) The ICH8 and ICH8R are differentiated from one another only by their support for RAID and AHCI. Intel implements SATA Native Command Queuing (NCQ) through AHCI, so the ICH8 also misses out on this worthwhile I/O performance enhancement. Interestingly, the nForce chipsets manage to support NCQ without AHCI.

Despite the fact that most south bridge chips support multiple RAID levels, there are a couple of key differences between the Intel and Nvidia storage controllers. Nvidia supports RAID 0+1 while Intel sides with RAID 10, for example. There's little difference between the performance of each array type, but RAID 0+1 arrays can handle a single drive failure, while RAID 10 arrays are capable of surviving the failure of two drives. The ICH7R and ICH8R also support Matrix RAID, which allows users to combine separate RAID 0 and 1 array partitions using only two drives. Intel recently updated its Matrix RAID software to support three- and four-drive configurations, giving users the freedom to create freakish hybrids such as a four-drive array that combines RAID 0 and RAID 5.

With the hard drive world firmly embracing Serial ATA, the need for IDE ports is diminishing quickly. So quickly, in fact, that Intel has dropped IDE support completely from its ICH8 family. Unfortunately, Serial ATA optical drives are few and far between, forcing motherboard makers to use auxiliary ATA controllers on motherboards featuring ICH8 chipsets. Those chips aren't necessary on boards with the ICH7R, nForce4 SLI X16, or nForce 570 SLI, all of which have at least one ATA channel.

Just about the only thing that suggests that the nForce 570 SLI is newer than the nForce4 SLI X16 is the fact that it joins Intel's chipsets in supporting High Definition Audio. The nForce4 is still capable of producing eight-channel output, but it's stuck with basic AC'97 audio and lacks support for HDA's sampling rates and resolutions. To be fair, though, anyone serious about truly high-definition audio (as opposed to the Intel-spawned marketing name "High Definition Audio") will probably want a discrete sound card with higher fidelity than motherboard audio implementations typically provide.

That leaves us with networking, and true to form, Intel prefers to let auxiliary chips handle Gigabit Ethernet rather than integrating it into the south bridge. That's not necessarily a bad thing, especially given the throughput and CPU utilization we've seem from some of Marvell's latest GigE chips on newer mobos. However, motherboard manufacturers don't always use the best networking chips, so there's some comfort in having a GigE controller integrated into Nvidia's nForce chipsets. Well, at least there's some comfort in having the nForce4 SLI X16's hardware-accelerated Gigabit Ethernet controller. We're not so keen on the nForce 570 SLI's lack of hardware TCP/IP acceleration, and apparently neither are motherboard manufacturers. The nForce 570 SLI-based Asus P5NSLI that Nvidia sent us for testing forgoes the integrated networking controller in favor of a Marvell chip.