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ATI's PCI Express Radeons previewed

A new spin for old chips

BACK IN MARCH, we explored ATI and NVIDIA's strategies for tackling the new PCI Express graphics standard. At the time, ATI touted the benefits of a native approach to PCI Express that eschewed bridge chips like NVIDIA's High-Speed Interconnect (HSI). ATI's native PCI-E implementation was certainly an elegant solution, but at the time the company didn't have much to say about specific PCI Express graphics products. Now, more than two months later, ATI is unveiling a family of PCI-E offerings that includes Radeon X800, X600, and X300 series graphics products. Those familiar with next-generation graphics will no doubt recognize the Radeon X800, but the X600 and X300 are new, sort of. Join me as I uncover what's new, what's not, and what's missing from ATI's PCI Express graphics lineup.

Radeon X800
ATI kicked its next-gen graphics offerings into high gear last month when it unveiled the Radeon X800 series graphics processors. Thanks to ATI's new R420 graphics chip, the Radeon X800s enjoy up to sixteen pixel pipes, six vertex engines, a 256-bit GDDR3 memory interface, and core clock speeds scaling beyond 500MHz. Today, ATI is spreading the X800 love to PCI Express with the R423 graphics chip. As far as pixel pipes, vertex engines, and memory interfaces are concerned, R423 is identical to R420. In fact, the only difference between the two chips is their graphics interface; R420 is AGP 8X while R423 offers a native PCI Express interface.

Although the R420 and R423 graphics chips are nearly identical, there are a couple of small differences between the PCI-E Radeon X800 series and their AGP equivalents. For starters, there is no direct PCI Express equivalent to the Radeon X800 XT Platinum Edition. ATI expects the first wave of PCI Express orders to be from OEMs, and the Platinum Edition is a little extreme for the likes of Dell. A PCI Express Radeon X800 XT will be available, though, just with a little less bling than the Platinum Edition.

In addition to dropping the Platinum Edition, ATI also indicated that PCI Express versions of the X800 Pro won't require an auxiliary power connector. The X800 XT will, however. A six-pin auxiliary power connector can be seen in an image ATI provided of a reference card:

Six-pin power on the top-right edge of the card

A look at the X800 XT reference card also reveals a pair of DVI output ports. We were crusading for dual DVI on high-end graphics boards long before it was fashionable, so it's good to see a dual DVI reference design. However, it's unclear how many PCI Express X800s will ship to OEMs with dual DVI ports, whether dual DVI will be limited to the X800 XT, and if retail boards from ATI or its partners will follow suit.

Radeon X600
For those who want PCI Express but don't need (or can't afford) a high-end X800, ATI is introducing a line of X600 mid-range graphics products with native PCI-E compatibility. Looking at the Radeon X600's name, one might assume that we're dealing with a cut-down version of the Radeon X800. However, apart from a 0.13-micron "Black Diamond" low-k fabrication process, the X600 actually has more in common with the Radeon 9600 XT than ATI's latest high-end cards.

The Radeon X600: PCI-E since way back in '03

Radeon X600 cards have actually been out in the wild as validation vehicles for PCI Express graphics since late last year, which explains why the X600's RV380 graphics chip is derived from the Radeon 9600 XT's RV360 core. For RV380, ATI has added native PCI Express support and some memory controller tweaks, but otherwise the chip's capabilities are unchanged¬óRV380 is still a 4x1-pipe design with two vertex shaders, its memory bus is still 128 bits wide, and it's still fabbed using a 0.13-micron low-k manufacturing process.

RV380 is so similar to RV360 that core clock speeds haven't changed with the new chip; the X600 XT's core is clocked at 500MHz like the Radeon 9600 XT, and the X600 Pro is clocked at 400MHz like the 9600 Pro. Memory clocks have been tweaked a little, though. The Radeon X600 Pro shares the same 600MHz memory clock as the 9600 Pro, but the X600 XT gets a memory clock boost up to 740MHz, yielding an extra 2.2GB/sec of memory bandwidth.