Chipset I/O performance
Now that we've flogged CrossFire's graphics performance sufficiently, let's take a quick look at the chipset's I/O performance to see whether we find a reprise of the USB and PCI Express Ethernet problems we found on Sapphire's implementation of the ATI Radeon Xpress 200 reference design.

Ethernet throughput
We evaluated Ethernet performance using the NTttcp tool from the Microsoft's Windows DDK. We used the following command line options on the server machine:

ntttcps -m 4,0,192.168.1.23 -a

..and the same basic thing on each of our test systems acting as clients:

ntttcpr -m 4,0,192.168.1.25 -a

We used our Abit IC7-G-based system as the server for these tests. It has an Intel NIC in it that's attached to the north bridge via Intel's CSA connection, and it's proven very fast in prior testing. The server and client talked to each other over a Cat 6 crossover cable.

The Ethernet tests are what they are, but they also serve as something of a proxy for general PCI Express x1 performance. In order to keep things even, we tested the nForce4 SLI's Ethernet throughput using a PCI-E x1 card bearing the exact same Marvell 88E8052 PCI-E GigE chip found on ATI's reference motherboard—with the exact same drivers. We also tested NVIDIA's built-in Gigabit Ethernet with ActiveArmor acceleration to see if it provides any benefits. Although we didn't test it in the review of the Sapphire board, I also decided to stress PCI performance using a PCI-based VIA Velocity GigE NIC.

It's redemption and disgrace all at once for the Radeon Xpress 200. This board shows none of the PCI Express throughput problems that we saw with the Sapphire board. In fact, the Radeon Xpress 200 CrossFire Edition turns in lower CPU utilization with the PCI-E NIC than the nForce4 SLI does. However, our decision to test with a PCI NIC has exposed another weakness: abysmal PCI throughput. Not everyone is going to care about ye olde PCI bus this day and age, but some folks will. I wouldn't want to rely on the Radeon Xpress 200's PCI implementation to host a GigE NIC, a RAID card, or an array of TV tuners in a home theater PC system, for instance.

NVIDIA's ActiveArmor TCP acceleration finally pays off in the form of lower CPU utilization. Too bad it took NVIDIA months and months into the life of the product to make it work as advertised.

USB performance
We used HD Tach to measure USB transfer rates to a Maxtor DiamondMax D740X hard drive in a USB 2.0 drive enclosure.

The Radeon Xpress 200's low USB transfer rates and relatively high CPU utilization persist. Like the slow PCI performance, this isn't a deal-killer unless you have some specific plans for high-throughput USB peripherals. Still, I'd prefer to see better performance here. It's possible that some of ATI's motherboard partners may opt to use ULi's Radeon Xpress 200-compatible south bridge in place of the SB450 in order to sidestep these problems.