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Radeon HD 4890 vs. GeForce GTX 275


Battle at two-fiddy
— 6:34 PM on April 6, 2009

AMD and Nvidia, those guys. Always with the competing, the one-upsmanship, the PowerPoint slides, the late-night phone calls before a product launch, the stake-outs, the restraining orders. Both sides want desperately to win the next round of the competition, to be ready to capture your business when the time comes for a video card upgrade.

And heck, both have very good products these days. In fact, the competition between them has been perhaps tighter than ever in the past little while. Since the advent of DirectX 10-class GPUs, we've seen image quality and feature sets converge substantially. With little to separate them, the two sides have resorted to an astounding bit of price competition. What you can get in a video card for under $200 these days is flabbergasting.

Since the introduction of its excellent Radeon HD 4000 series, AMD has been doing most of the driving in the market, setting standards for price and performance and forcing Nvidia to follow suit. For its part, Nvidia has acted very aggressively to remain competitive, slashing prices and rejiggering products at will. So it is now, with the introduction of a brand-new GPU from AMD, the Radeon HD 4890, and the rapid-response unveiling of a similarly priced competitor from Nvidia, the GeForce GTX 275. Both cards are slated to sell for around 250 bucks, and they are among the fastest single-GPU graphics cards on the planet.

Which is better? Tough to say. We have only had a short time with each card, but we've put them head to head for a bit of a comparo, and perhaps we can begin to answer that question with this quick first look.


In the red corner: Radeon HD 4890
The GPU that powers the Radeon HD 4890 is something of a curiosity. This chip, code-named RV790, shares the same architecture with the RV770 GPU you'll find in the Radeon HD 4850 and 4870, and it's made on the same 55nm manufacturing process. Yet the RV790 is very much a new chip, in spite of the similarities. Why the new design? AMD says it was reaching "an odd plateau" with RV770 clock speeds, and the modifications to the RV790 are intended to resolve that problem, enabling higher clock frequencies and thus better performance.


The Radeon HD 4890

To that end, AMD's engineers endowed the RV790 with a new row of decoupling capacitors around the perimeter of the chip, as apparent in the overlay image on the right. (That red ring around the chip signifies the capacitor placement, not death, Xbox 360 fans.) The caps ought to lower noise and improve signal quality, allowing the chip to better tolerate more voltage. In addition, AMD has reworked the chip's timing and power distribution with an eye toward higher clock speeds.

The tweaks make for a slightly larger piece of silicon: the RV790 measures out to about 17 mm per side, by my little green ruler, or roughly 290 mm². The RV770, by way of comparison, is 260 mm². The transistor count is up, as well, from an estimated 956 million in the RV770 to 959 million in the RV790.

Happily, the changes appear to have worked. On the Radeon HD 4890, the RV790 is good for at least another hundred megahertz. AMD has set stock clock speeds on the Radeon HD 4890 at 850MHz (versus 750MHz for the 4870), and this time around, the firm seems to have left some additional headroom for board vendors to offer higher clocked variants—or for overclockers to exploit, perhaps. GDDR5 clock speeds are up, as well, from 900MHz on the stock Radeon HD 4870 to 975MHz on the 4890. That may sound like a modest increase—and to some extent, it is—but keep in mind that GDDR5 memory transfers data four times per clock, so even smaller increments can add up. Also, 4890 cards come with a gigabyte of memory onboard, double the standard payload of most 4870s.

AMD estimates the peak power draw of a Radeon HD 4890 card at about 190W, but power consumption at idle should be lower than the 4870's, at around 60W, thanks in part to board design alterations and in part to chip-level modifications.


A closer look at the RV790 GPU

As I've said, the 4890 is priced at around 250 bucks, but these days, nothing's quite that simple. You'll find a number of 4890 cards listed at online vendors for $249.99. This XFX model is a good example. But most of 'em, like the XFX, have a $20 mail-in rebate attached. So hey, if you can write small enough to fill out one of those forms, and if the postal service doesn't lose it, you have a chance at getting a $20 check two or three months from now. That's not your only option, either. The card we've tested, for example, is a Sapphire offering with a 900MHz GPU clock that's selling for $264.99 and also comes with a $20 mail-in rebate. Oddly enough, AMD classifies any Radeon HD 4890 card clocked at 900MHz or better as separate product, dubbed the "Radeon HD 4890 OC," although clock speeds on those cards will vary. We've thus labeled the product we've tested as a "4890 OC" in our benchmark results. We'll get into the exact amounts of GPU capacity and bandwidth involved shortly, but whichever 4890 card you choose, that's a heck of a lot of power for the money.

The 4890's debut raises a couple of questions. One is whether the RV790 will be migrating to the lower rungs of the Radeon HD 4800 series product lineup, as sometimes happens in cases like these. AMD says the answer is no, that the Radeon HD 4850 and 4870 will always be based on the RV770, because the RV790 is a larger chip (and thus almost assuredly more expensive to produce). We should see 1GB versions of the 4870 and 4850 become more prominent going forward, though.

Another obvious question: will we see a Radeon HD 4890 X2 card soon? AMD told us it doesn't have plans for such a beast at this time, in part because putting two RV790 GPUs on a board, with each at 850MHz, would result in total power consumption north of 300W. That's great news for power supply makers but an inconvenience for everyone else. A 4890 X2 could still happen, though, if AMD deems it viable, so we'll have to wait and see.