Under the south bridge
In the past, ATI has collaborated with ULi, the artist formerly known as ALi, for its south bridge chips, but ATI says the Radeon Xpress 200 south bridge is an "all in-house design." ULi will apparently offer a south bridge chip for the Radeon Xpress, as well.

Hmmmm.

ATI's south bridge chip, fabricated on TSMC's 180nm process, is nothing too special. It has no PCI Express lanes, with the exception of the two it uses to talk with the north bridge. The rest of the PCI-E I/O will be handled by the four extra lanes on the north bridge. The table below gives a quick summary of the south bridges expected to be paired up with the first wave of PCI-E chipsets. One caveat, though: the VT8251 south bridge will probably not arrive in time for early K8T890 boards, so VIA's older VT8237 will probably serve on those boards, instead.

I've omitted some not-terribly-exciting but necessary south bridge bits, like the LPC interface for keyboards and serial ports, but rest assured all of the chipsets above have them. I'm just sticking to the highlights.

The Xpress 200 south bridge has many of the latest goodies, but it's not aiming for best-in-class status on the basis of specs. It has four ports of Serial ATA storage capability, but it lacks the new SATA-II extensions for hot-plugging devices, Native Command Queuing, and 300MB/s transfer rates. Of those three, NCQ is the biggest loss; NCQ can really boost disk I/O performance in heavy use, especially when multitasking, as our benchmarks have shown. Without it, SATA drives are knocked out of the ranks of SCSI-class performance.

ATI's south bridge also has support for RAID, but only levels 0 and 1, not the sweet combo of striping plus mirroring, RAID 0+1. And unlike the nForce4, ATI's south bridge can't do RAID with ATA drives or span arrays between ATA and SATA drive types.

ATI's Radeon Xpress 200 reference board

Audio is also nothing special. ATI has given the south bridge eight audio channels, but only for AC'97 audio. Intel's High Definition Audio standard, also known as Azalia, isn't supported. Don't go looking for any sort of 3D positional audio, either. ATI hasn't given the Xpress 200 any sort of hardware acceleration for such algorithms, and in fact, the drivers for ATI's audio won't do 3D sound in software, either. It's possible that drivers for external audio codecs, like the Realtek ALC655 present on the ATI reference board, will add software-level positional audio capabilities on production boards. That's how it generally works with other chipset brands.

Incidentally, ULi's south bridge for the Radeon Xpress 200 will include High Definition Audio capability, so it may prove to be a popular option.

ATI has opted not to include any form of Ethernet controller on the Xpress 200 south bridge. This is quite the departure from NVIDIA's ambitious plans for built-in Gigabit Ethernet and a hardware-accelerated firewall, but ATI reckons PCI Express will handle networking chores, including Gigabit Ethernet, just fine, thanks.

ATI's business plan for the Xpress 200
ATI says the Radeon Xpress 200P will be priced above chipsets from VIA (no surprise, since VIA has long been the low-cost choice) but below the highest-end chipset from NVIDIA. The company is quick to emphasize that the IGP version of the Radeon Xpress 200 has virtually no competition. VIA does plan a version of the K8T890 with integrated S3 DeltaChrome graphics that could give it a run for its money—eventually. NVIDIA is also apparently planning an IGP based on GeForce 6-class graphics technology, but that chipset isn't expected to arrive for a while, either. For now, the Radeon Xpress 200 has the market for Athlon 64 chipsets with integrated graphics and PCI Express all to its lonesome. ATI will likely price the IGP version of the Xpress 200 accordingly.

As is characteristic for ATI, the primary focus for Radeon Xpress 200 sales will be big system builders, or OEMs. Retail boards will come later from MSI, among others. ATI is hoping to help AMD crack the market for corporate desktop PCs in large enterprises—a Sisyphean task if ever there were one, but perhaps they know something I don't. ATI's other emphasis for OEM sales, entertainment PCs based on Windows XP Media Center Edition, is probably more of a sure thing. This chipset makes perfect sense for MCE systems, and ATI says it's exploring the possibility of putting a Rage Theater 550 chip on the motherboard or elsewhere in the system to assist with high-definition video handling. Obviously, ATI has a strong hand to play here, and I'd be surprised not to see them chalking up some design wins. However, they're mum on design wins right now, saying that they'll be ready to talk more about it early next year.

The Radeon Xpress 200 has potential beyond the desktop and living room, of course, and ATI claims it's working toward getting workstation and server products built on its chipsets. We'll see whether or not they materialize. A mobile version of the Radeon Xpress 200 is in the works, as well, as is a family of PCI Express chipsets for the Pentium 4. I couldn't shake loose any more specifics about either yet, though.

Let's move on to our test results.