DarkRagnorak........
Like most Athlon 64 chipsets, the Radeon Xpress 200 series will talk to AMD Athlon 64 (and Sempron and perhaps Opteron) processors via a HyperTransport link. That link is 16 bits in each direction, with a clock speed of up to 1GHz. Because the latest AMD processors have their own memory controllers onboard, the Radeon Xpress 200 north bridge chips should perform in memory-bound tasks about like most other chipsets do when paired with an AMD K8-class processor. Thus, the bulk of the north bridge's uniqueness comes from other features, like PCI Express and integrated graphics.
Below is a quick feature summary of the new PCI-E north bridges. The asterisk next to the HyperTransport speed on the nForce4 is intended to denote a possible problem. NVIDIA says it will have a full 1GHz HyperTransport link, and we believe it, but rumors to the contrary just won't go away. We're sticking an asterisk in there just in case.
Intel 915G/925X VIA K8T890 ATI Radeon Xpress 200 NVIDIA nForce4 Ultra
HyperTransport link N/A 16-bit/1GHz 16-bit/1GHz 16-bit/1GHz*
PCI Express lanes 16 20 22* 20
North/south bridge interconnect type DMI Ultra V-Link 2 lanes PCI Express N/A (Single chip)
Peak theoretical interconnect bandwidth 2GB/s 1.06GB/s 1GB/s N/A (Single chip)
The Radeon Xpress 200 north bridge has a hefty 22 lanes of PCI Express connectivity. (Lanes are the bidirectional pairs of point-to-point communication links that make PCI Express work; each lane offers 250MB/s of bandwidth in each direction.) 16 of those lanes will be dedicated to a PCI-E X16 graphics slot in a typical configuration, while two of them on the Radeon Xpress 200 are dedicated to act as links to the south bridge. That leaves four lanes free to service on-board peripherals or PCI-E X1 slots.
ATI says the Radeon Xpress 200 could, in fact, serve as a competent chipset for a motherboard capable of hosting an NVIDIA SLI config by dedicating eight PCI Express lanes each to a pair of PCI-E X16 slots, just as other SLI motherboards reportedly will. I don't doubt that such a thing is technically possible, but I'll believe it's happening when I have a production motherboard in my sweaty little hands.
The other bit of PCI Express related goodness you may be interested to learn about is related to overclocking. ATI says the Radeon Xpress 200 can indeed lock the PCI-E clock at standard speeds while the rest of the system (primarily the HyperTransport link, which controls CPU and memory clock speeds) is being overclocked. That opens up the possibility of some fairly decent enthusiast's motherboards based on the Radeon Express 200P showing up.
Hope this answers your question .
dl65
