The CrossFire Xpress 3200 Chipset
The ATI CrossFire Xpress 3200's main selling point is that the chipset features 32 dedicated PCI Express lanes for graphics, double the number of their previous solution. As we mentioned earlier, the older Radeon Xpress 200 chipset has only 16 lanes dedicated for graphics. This is fine for a single-video card configuration, but when running a system in CrossFire mode, that meant the lanes had to be split, and each PEG slot only had an x8 electrical connection. Obviously, this is no longer the case with the CrossFire Xpress 3200.
According to ATI, the CrossFire Xpress 3200 chipset went from the design phase to full production in only 8 months. And with first silicon it took only 24 hours to get CrossFire up and running reliably in their labs. No small feat considering the chip consists of over 22 million transistors, but then again, ATI does have some experience in the chipset arena. The company ships hundreds of thousands of chipsets a month for the desktop and notebook markets.
ATI is also quick to point out that the CrossFire Xpress 3200 has the smallest Northbridge die on the market today, at roughly 39mm2. As you can see, in the picture on the left, the die is quite small. The CrossFire Xpress 3200 die is so small because it is manufactured on TSMC's 0.11 micron low-K process node. Using TSMC's .11 low-K process also helps ensure the chip requires less power to operate reliably. In this case, ATI is claiming a TDP of 8 Watts for the CrossFire Xpress 3200.
Because ATI's new northbridge has double the number of PCI Express lanes dedicated to graphics, each PCI Express x16 slot always has an x16 electrical connection to the chip, for double the amount of peak bandwidth, up to 8GB/s in this case. We should also point out that all of the CrossFire Xpress 3200's PCI Express lanes reside in a singe chip. Motherboards based on NVIDIA's nForce 4 SLIX16 chipset also have two PEG slots, both with x16 electrical connections, but half of the PCI Express lanes connect to the chipset's northbridge (SPP), and the other half connect to the southbridge (MCP). In situations where data is swapped between the graphics cards, the data has to travel between the two chips, which could be a bottleneck is some situations, for example when running a pair of low or mid-range cards in SLI mode, especially when cards are not equipped with an SLI edge connector.
According to ATI, the CrossFire Xpress 3200 allows X1600 and X1300 cards running in CrossFire mode to scale better than their previous chipsets, because each card has more available bandwidth to work with for inter-card communications. On the other hand, with high-end X1800 and X1900 Crossfire solutions, data is shared via the compositing engine over the CrossFire dongle, so in this scenario there is no possibility for bandwidth limitation, at least over PCI Express links. All of this however, is not as easy to prove out, as one might think, in current real-world 3D render scenarios. So at the end of the day, overall performance metrics are really all we have to work with. And of course we'll be providing those for you as well in the pages that follow.