In the green corner: GeForce GTX 275
You didn't really expect Nvidia to sit back and watch passively while AMD unveiled its hot new graphics card, did you? The green team already has the fastest single-GPU card in the form of the GeForce GTX 285, and meeting the 4890 head on was merely a matter of spinning out a new variant. That product, we have learned, will be called the GeForce GTX 275, and although cards won't be available in all parts of the world until April 14, we have an early sample of the GTX 275 in Damage Labs for comparison against the new Radeon.
Happily, in order to compete with the Radeon HD 4890, the GeForce GTX 275 had to be a pretty potent product, so Nvidia has left a large fraction of the GTX 285's computing and graphics power intact. Like its elder sibling, the GTX 275 is based on the 55nm version of the GT200 GPU, and it has all 240 of its stream processors enabled. The only major concession Nvidia has made to product segmentation is the disabling of one of the chip's ROP partitions, which reduces its fill rate from 32 pixels per clock to 28, with an attending drop in antialiasing throughput.
With that change, the GPU's total memory interface width is also reduced from 512 to 448 bits, and the total RAM available drops from 1GB to 896MB. (You'll see 14 rather than 16 chips in the picture above for this same reason.) 448 bits is still nearly twice the width of the 4890's 256-bit path to memory, but Nvidia uses GDDR3 RAM, which only transfers data twice in each clock cycle.
The GT200 architecture is different in other ways, too, including the fact that its shader processors run at higher frequencies than much of the rest of the chip. For the GTX 275, Nvidia has settled on a core clock of 633MHz, SPs at 1404MHz, and GDDR3 memory at 1134MHz. Those clock speeds and the total theoretical GPU power involved are both down somewhat from the GTX 285, but they're still considerableand very much in the same class as the Radeon HD 4890, as we'll soon see.
The de-tuning of the 55nm GT200 GPU has power consumption benefits: Nvidia rates peak GTX 275 board power at 219W, down over 60W from the GTX 285. That's a little more power-hungry than the Radeon HD 4890, but the 55nm GT200 is a larger chipthe metal cap covering the package in the picture above obscures its exact size, but it has a heart-stopping 1.4 billion transistors. And the card itself has nearly twice as many memory chips onboard. Fortunately, recent GeForces have had admirably low power draw at idle, and the GTX 275 ought to continue that tradition.
GTX 275 cards aren't yet selling on these shores, but Nvidia claims they should go for $249, by which it surely must mean $250 minus a penny. That puts 'em solidly into Radeon HD 4890 territory, but we'll have to watch and see how mail-in rebates, game bundles, and price premiums for higher-speed models pan out. I should note that we're testing a reference board with a stock clock speed in this review, so some GTX 275 models may offer slightly higher performance.
Side by side
Dude, look: pictures!