Comparing chipset specs
Before diving into our performance tests, we've whipped up a couple of handy spec comparison tables that contrast the CrossFire Xpress 3200 and nForce 590 SLI with leading Socket 939 chipsets. The north bridge is up first, and since the same CrossFire Xpress 3200 chip is used for Socket AM2 and 939 platforms, we've only listed it once.

Note the huge disparity in the number of north bridge PCI Express lanes between the CrossFire and nForce chipsets. NVIDIA makes it up at the south bridge, of course, and perhaps that's why the nForce4 SLI X16 and 590 SLI have a much higher bandwidth speed chipset interconnect than the CrossFire Xpress 3200.

Next, we turn our attention south. We've added the ATI SB450, ULi M1575, and NVIDIA nForce4 SLI X16 MCP to accompany the south bridge components of our Socket AM2 chipsets.

The nForce 590 SLI's cornucopia of PCI Express lanes, Serial ATA and Gigabit Ethernet options, and supported RAID levels looks mighty impressive when compared with what ATI offers with the SB600. Still, the SB600's array of south bridge features should be enough for most folks, especially when paired with a decent PCI Express Gigabit Ethernet chip or two.

Note that while both the SB600 and nForce 590 SLI support Native Command Queuing (NCQ), only the SB600 does so through Intel's Advanced Host Controller Interface for Serial ATA. NVIDIA has supported NCQ since the nForce4, but eschews AHCI in favor of a proprietary spec it developed before AHCI existed. According to NVIDIA, its approach offers better performance with no real penalties because AHCI is just a register-level interface spec. NVIDIA's approach offers another perk in that additional drivers aren't necessary to install Windows XP to a single Serial ATA drive; auxiliary drivers are required to install Windows to drives running in AHCI mode on the SB600. That will become a non-issue when Vista arrives because both ATI and NVIDIA are promising to have in-the-box drivers for Microsoft's next operating system.

Microsoft drivers are actually responsible for the asterisk beside the nForce4 SLI X16 MCP's support for ATA RAID. The chipset initially supported RAID for ATA devices, but Microsoft apparently didn't take too kindly to its mass storage controller driver being used for a RAID device. Rather than taking on Redmond, NVIDIA has dropped support for ATA RAID on newer nForce4 chipsets, and left it out of the nForce 590 SLI. RAID isn't really worth it on a single ATA channel, anyway.