ATI Xpress 3200 / RD580
RD580, outwardly known as Xpress 3200, is one of John Bruno's team's creations. The ATI ASIC Design Manager and his guys have spent good time making sure the northbridge kicks some ass for the overclocking and performance enthusiast, while at the same time doing good things at more mundane and standard clocks.
Crossfire performance was near the top of the list of priorities, too. Without the luxury of an inter-board link like NVIDIA and SLI, and a fairly clunky exterior cable solution not ideal, moving the board-to-board comms entirely onto the mainboard and PCI Express implementation was a needed investment. A coming CATALYST driver release will make Crossfire master hardware obsolete and Xpress 3200 is kingpin to that working.
Xpress 3200 supports PEG16X dual graphics, as RD480 did, but this time all the lanes come from the northbridge IC. ATI make a big deal about Xpress 3200 supplying dual x16 graphics from a single chip, compared to NVIDIA who need a second chip for x16 SLI. While NVIDIA's solution isn't exactly slow, it makes sense that keeping the comms between boards on-chip (and on fast paths inside that chip, too) will ultimately be quicker.
Xpress 3200 therefore provisions 40 PCI Express lanes, 36 usable by the system with that split into 32 for graphics and 4 for general PCI Express I/O. The remaining 4 lanes are for communications with any southbridge I/O processor (ATI call that Alink2).
There's also the HyperTransport implementation needed for communication with the CPU. And that's pretty much it, actually, which goes a fair way to explaining why the resulting silicon is bare millimetres wide and comprises just under 22 million transistors.
The southbridge issue
When talking about a new chipset there's usually some chatter about a new southbridge to he had. Not this time, though, with ATI delaying the release of their brand new SB600 southbridge until later in the year, seemingly because it's just not finished yet. So that leaves board vendors looking to create an Xpress 3200-based systems with the choice of ATI's existing SB450 or SB460 southbridges (SB460 is SB450 with pin compatibility with SB600 for when that finally appears, easing a new product introduction), or something like ULi's M1575.The M1575 seems like the popular choice, connecting via Alink2 and supplying HD Audio, a modern PCI Conventional implementation, SATA2 disk controller (with RAID support), PCI Express lanes, eight USB2.0 ports and a 100Mib/sec Ethernet controller in one 31mm² BGA package.
Summary
Xpress 3200 seems like the consumate modern northbridge that supports AMD Athlon 64 processors (including FX and X2). 40 on-chip lanes of PCI Express facilitate same-chip dual graphics and extra peripheral expansion, and the focus on the overclocker and running the IC at significantly inflated speeds was a consideration since day one.Southbridge choice is just that, the vendor getting to pick what they think is right for their particular board, with M1575 the likely choice (and a fine one at that).
So if the basic on-paper specs are sound, then, it's all down to implementation after that. Let's peek at the ASUS A8R32-MVP first.