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. GDDR5 clock speeds are up, as well, from 900MHz on the stock Radeon HD 4870 to 975MHz on the 4890. 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. On the Radeon HD 4890, the RV790 is good for at least another hundred megahertz. Happily, the changes appear to have worked. The transistor count is up, as well, from an estimated 956 million in the RV770 to 959 million in the RV790. The RV770, by way of comparison, is 260 mm². 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. In addition, AMD has reworked the chip’s timing and power distribution with an eye toward higher clock speeds. (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. 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. 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. Yet the RV790 is very much a new chip, in spite of the similarities. This chip, code-named RV790, shares the same architecture with the RV770 GPU you’ll find in the Radeon HD 48, and it’s made on the same 55nm manufacturing process. The GPU that powers the Radeon HD 4890 is something of a curiosity. 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. Both cards are slated to sell for around 250 bucks, and they are among the fastest single-GPU graphics cards on the planet. 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. For its part, Nvidia has acted very aggressively to remain competitive, slashing prices and rejiggering products at will. 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. What you can get in a video card for under $200 these days is flabbergasting. With little to separate them, the two sides have resorted to an astounding bit of price competition. Since the advent of DirectX 10-class GPUs, we’ve seen image quality and feature sets converge substantially. In fact, the competition between them has been perhaps tighter than ever in the past little while. 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.Īnd heck, both have very good products these days. 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.
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