AMD'S LATEST ATHLON 64 processors use a new socket and DDR2 memory, essentially requiring a motherboard upgrade. It just wouldn't do to plug a cutting-edge processor into a motherboard with an older chipset, though. Perhaps that's why ATI and NVIDIA are rolling out new core logic to accompany AMD's Socket AM2. In the green corner, NVIDIA is launching a top-to-bottom line of nForce 500 series chipsets, including the high-end nForce 590 SLI. ATI, on the other hand, is finally taking the wraps off its long-awaited SB600 south bridge. That chip is paired with the established CrossFire Xpress 3200 north bridge for high-end multi-GPU platforms.

In many ways, the latest core logic offerings from ATI and NVIDIA are evolutionary designs that address problems with previous chipsets. ATI claims its SB600 resolves the I/O performance problems that plagued the SB450, and NVIDIA promises the nForce 500 series' Gigabit Ethernet acceleration sheds the hardware bug that afflicted the nForce4's ActiveArmor. New features are also on the menu. The SB600 is ATI's first stab at Serial ATA with 300 MB/s and Native Command Queuing, and the nForce 500 series is virtually bursting at the seams with fancy feature names, including FirstPacket, LinkBoost, and DualNet.

Is the combination of ATI's CrossFire Xpress 3200 and SB600 potent enough to prevent NVIDIA's nForce 590 SLI from inheriting the Athlon 64 core logic crown? We've subjected both chipsets to an exhaustive array of application, peripheral, and power consumption tests to find out, and the answer might surprise you.

ATI's CrossFire Xpress 3200 for AM2
Oddly enough, the north bridge component of ATI's CrossFire Xpress 3200 for AM2 chipset isn't new at all. It's the same chip ATI introduced several months ago for Socket 939, but this time around, it's connected to Socket AM2. The chip offers 40 lanes of PCI Express connectivity, allowing it to feed two full-bandwidth PCI-E x16 slots. ATI has made much of this capability, claiming that multi-GPU configurations that hang one graphics card off the south bridge suffer from poor performance due to limited chipset interconnect bandwidth. Consolidating all of a chipset's PCI Express lanes in the north bridge is certainly a much cleaner approach, but the performance of NVIDIA's nForce4 SLI X16 chipset certainly doesn't seem to suffer due to its dual-chip layout.

The multi-GPU configuration most likely to benefit from having both graphics cards hanging off the north bridge would be one that relies solely on PCI Express to pass data between cards. That type of setup is only common with low-end graphics cards, though; high-end configs use a CrossFire dongle or SLI bridge connector to pass data between graphics cards, largely bypassing PCI Express. Since the CrossFire Xpress 3200 is a high-end chipset, it's unlikely to be paired with the kind of low-end or even mid-range graphics cards that stand the best chance of benefiting from its PCI Express configuration.

With 32 of the CrossFire Xpress 3200's PCI Express lanes occupied by a pair of 16-lane graphics slots, eight lanes remain. Half are available to PCI Express peripherals and x1 slots, with the last four reserved for ATI's Alink2 chipset interconnect.

Using standard PCI Express lanes for a chipset interconnect allows the CrossFire Xpress 3200 north bridge to easily interface with a range of south bridge chips, including ULi's M1575. The M1575 was a popular way for motherboard manufacturers to avoid the liabilities associated with ATI's older SB450 chipset, but with NVIDIA's recent acquisition of ULi, the arrival of ATI's new SB600 south bridge is particularly timely.

With the SB600, ATI claims it has addressed the I/O performance issues that plagued the SB450. There's more to the SB600 than just performance improvements, though. ATI has also added features, including support for 300 MB/s Serial ATA transfer rates and Native Command Queuing to the chip's SATA controller. That controller's RAID capabilities have also been bolstered, with ATI adding support for four-drive RAID 10 arrays to complement RAID 0 and RAID 1. It's a little disappointing that RAID 5 didn't make the cut for the SB600, but given the poor write performance we've seen from several chipset-level RAID 5 implementations, it's not a huge blow to the SB600's appeal.

With the exception of RAID 5, the SB600 has everything else you'd expect from a modern south bridge chip, including support for AC'97, High Definition Audio, and 10 USB ports. A single ATA channel has also become the norm, for better or worse, limiting users to just a pair of parallel ATA devices. At the very least, the limited number of available ATA channels in new core logic chipsets should encourage optical drive manufacturers to offer a greater number of Serial ATA options.

One thing you won't find in the SB600 is a networking component. ATI doesn't even integrate a basic 10/100 Fast Ethernet controller, instead relying on motherboard manufacturers to offer Ethernet options via PCI or PCI Express. There are some pretty spiffy PCI-E Gigabit Ethernet controllers out there, so a lack of integrated networking isn't necessarily a strike against the SB600. However, some GigE chips have less attractive performance characteristics, so prospective buyers have to be careful about which chip a mobo maker chooses to integrate.

ATI's CrossFire Xpress 3200 for AM2 came to us riding a fancy-pants reference board with a white base and red trim. Look beyond the fancy colors, though, and it's worth paying special attention to the reference design's tiny passive coolers. ATI's core logic chips have a reputation for running cool, and the Xpress 3200 and SB600 are no exception. The former is built using 90-nano fabrication technology and requires little more than a tallish passive cooler. The SB600's heat output—or lack thereof—is even more impressive. That chip is built using an older 130-nano process, but it makes do with just a tiny low-profile cooler.