Chipset analysis
There's quite a bit of new technology to cover with the XPRESS 200. I'll take a look at it in conjunction with the ubiquitous chipset block diagram.
As you can see, ATI has gone with a traditional two-chip design here, breaking it down to north and south bridges. Pre-Athlon 64, north bridges were used as an interconnect/controller to main system memory and, concurrently, to a graphics interface, usually 8x AGP. Athlon 64 CPUs changed the face of north bridge design by accommodating the memory controller directly on the CPU itself, which then talked to system memory directly. This also had the knock-on effect of making chipset design for the likes of VIA and NVIDIA into a simpler affair; AMD had done the harder part for them. Leading on from this was a lack of performance deviation between rival chipsets, because AMD had essentially taken away an obvious area of chipset-level optimisation.
XPRESS 200 North Bridge
ATI's decided that the Athlon 64's peculiar architecture and excellent performance would be the perfect base for a do-it-all chipset. It has thus split its XPRESS 200 into two groups; one with an integrated graphics core (XPRESS 200) and one without (XPRESS 200P). The processor hooks up to the north bridge via a 1GHz 16-bit HyperTransport link. That's pretty much par for the course. It seems as if all non-Intel PCIe chipset designers favour having peripheral PCI-Express lanes off the north bridge. ATI makes do with 4. Also, note the interconnect between bridges is actually 2 PCIe lanes (500MB/s each, 1GB/s in total) and not a company-specific link. That pushes up the total PCIe lanes to an impressive 22.
The term integrated graphics conjures images of lobotomised performance and inability to even run the latest games. Here's where the XPRESS 200 shines, relatively speaking. ATI has always been of the thinking that integrated graphics should offer more than just simple video-out. The XPRESS 200 IGP is actually a based on the current X300 core and therefore is a full DirectX9 part, replete with support for Pixel and Vertex Shader 2.0 specification. From what I can gather from ATI's documents, it also supports up to 6x multisampling-based AntiAliasing (read no discernible edges), full-precision floating-point pixel pipeline (read realistic-looking colour). Two pixel pipelines operate at a core speed of up to 350MHz, and each one has a single texturing unit. Sure, it's not going to trouble a discrete midrange PCI-Express card, but that's not its aim, is it?. At least you'll be able to play all those lovely demos that make use of DX9's advanced feature set.
ATI has also done something not seen before with an IGP setup. Dubbed HyperMemory, ATI gives the end-user the choice of either stealing the IGP's bandwidth from main system memory or, optionally, the use a dedicated local framebuffer, in the form of motherboard-embedded memory, through either a 32- or 64-bit path. It can also be used in tandem with system memory, interleaved, for better performance. A local framebuffer makes sense when system RAM is minimal, say, 256MB, but the added cost of embedding it may push potential customers away. We'll have to wait for retail pricing before this question can be answered accurately. I'll be testing just how effective ATI's interleaving IGP mode is, too.
Leading on from the 3D qualities of the XPRESS 200 IGP is SURROUNDVIEW, ATI's multi-monitor feature that allows the IGP's video-out, through both DVI or VGA and up to 1600x1200, to work in conjunction with an ATI-based discrete PCI-Express card. That's a potential 4 displays if you can use both the IGP's and discrete card's twin outputs. However, it's not possible to use the IGP for concurrent CRT and TV-Out, unfortunately. As you would expect, the PCI-Express lane for graphics subscribes to the industry-standard x16 protocol. All in all, the IGP version of the XPRESS 200 is an intriguing proposition.
XPRESS 200 South Bridge
Just to re-iterate, the south bridge communicates with its neighbour via a conduit made up of 2 PCI-Express lanes. That's the only 2 you'll find, as peripheral lanes emanate from the north bridge. 4 on-chip SATA ports have become the norm these days, but ATI's south bridge supports only RAID0 and/or RAID1. That puts it behind the RAID0+1 support afforded by the likes of NVIDIA's nForce4 and VIA's VT8251 south bridges. There's also no Native Command Queuing, as found on both aforementioned bridges. Sound output is also at its most basic level. 8-channel AC'97 has been around for a while now, so it's a shame for ATI not to adopt a higher-quality output. It's certainly not as well-featured as the nForce4, and the chipset seems a little lopsided to me. Most of the feature action is limited to the all-new north bridge. Thinking about it for a second, the south bridge could have fitted into a chipset designed 18 months ago.
