The Radeon Xpress 200P chipset was launched in late 2004, with the Crossfire Edition RS480 following late last spring. However, things did not go the way ATI wanted, because the dual graphics spin-off did not arrive before October this year. Still, as they say, good things come to those who wait.

The basic characteristics are all close to what we already know from the Radeon Xpress 200P single graphics chipset. All types of Socket 939 processors are supported, including the Athlon 64, Athlon 64 X2 and Opteron for Socket 939. Dual Channel DDR400 memory support is a chipset default. The north bridge has a total of 16 PCI Express (PCIe) lanes, which usually are configured to power two x16 PCIe slots at x8 bandwidth each. While NVIDIA's double-x16 nForce4 SLI chipset is already around, ATI is currently working on upgrading the Radeon Xpress. Currently, all additional PCI Express lanes for components such as Gigabit Ethernet are provided by the north bridge itself, while most other chipset vendors prefer to run these through the south bridge; either way works.

When it comes to storage interfaces and features, networking, audio and USB 2.0 ports, ATI depends on its suppliers. Although there are ATI's SB400 and SB450 south bridge components, these still don't provide state-of-the-art features such as Serial ATA II speeds (300 MB/s) and Native Command Queuing support. Until the SB600 ships sometime in early 2006, chipset supplier ULi's M1575 is used as an alternative. Since ATI links up its north and south bridge via PCI Express, any compatible device can be used. Finally there is a software detail that some users consider a disadvantage: Microsoft's .net framework is required for ATI's driver set.

ULi Contributes The Crossfire South Bridge

The ATI south bridge SB450 supports twin UltraATA/133 channels; four SATA/150 ports with support for RAID 0, 1 and 0+1; integrated 7.1 sound audio with support for high definition modes; a 32 Bit PCI controller; and eight USB 2.0 ports. However, it lacks support for Serial ATA II features, RAID 5 and Gigabit Ethernet.

ULi's M1575 does offer a fully featured Advanced Host Controller Interface (AHCI) Serial ATA controller that meets the SATA 2.5 specs, including 300 MB/s per-channel speeds and NCQ support. Still, it does not implement a Gigabit Ethernet controller, likely due to silicon costs.

ULi must be thankful for ATI picking PCI Express to hook up the north and south bridge components. The RS480 Radeon Xpress 200 chipset family won't link these two components with more than two PCI Express lanes, providing 500 MB/s of bandwidth both upstream and downstream. However, the M1575 is able to use four lines, which would effectively double the bandwidth.