The GTX 200 series are big boards with suitably bulky price tags. At first glance, then, it certainly looks like ATi has opted not to compete.
Its new Radeon HD 4800 series is a more restrained effort weighing in at just 956 million transistors and 260mm squared, the latter figure aided by the use of a slightly finer 55nm production process. It's an altogether smaller, less costly GPU to manufacture.
Initially, there are two boards in ATi's new line up, the 4850 (read our review here) and 4870 (review here). Both share the same number of functional units and are specified with 512MB of graphics memory. The key differentiators are clock speeds.
Fast clocks
The 4850 runs a core clock of 625MHz and a memory frequency of 2GHz while the 4870 ups the ante to 725MHz and 3.6GHz. The 4870's startlingly fast memory speed is courtesy of the first ever use of GDDR5 memory on a consumer graphics card. As for pricing, the 4850 model starts at £125 while the 4870 is a £200 board.
Here's the twist, though. Despite the smaller die size, transistor count and pricing, the new 4800 family comes awfully close to Nvidia's big beast in terms of raw capability. In fact, it actually outpoints the GTX 280 for pure computational grunt, if not 3D rendering throughput. The top spec Radeon HD 4870 board is rated at a monstrous 1.2TFLOPs where the GTX 280 manages just 933GFLOPs.
The secret
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To understand how ATi's new GPU pulls that trick off, consider the following facts.
Compared with the existing Radeon HD 3800 series, the 4800 family has nearly triple the number of shaders (800 to be precise, but note that ATi and Nvidia's shaders are not directly comparable) and texture units. And yet its transistor count has risen by just 44 per cent. In other words, what AMD has done with the 4800 series is far more sophisticated than creating an oversized 3800 core.
Every aspect of the chip's architecture has been overhauled with a view not just to performance but also to efficiency. That includes the welcome re-introduction of standard box-filter algorithms for anti-aliasing.
With the launch of the Radeon HD 2900 series early in 2007, AMD dabbled with a new 'adaptive' approach towards smoothing the jagged edges of rendered objects. In theory, it was more sophisticated. In practice, it was just plain slow.
Green flagship
A further benefit of ATi's focus on efficiency is power consumption. Nvidia's GTX 280 guzzles up to 236W, while the flagship Radeon HD 4870 consumes up to just 160W. Also, of the two big players in PC graphics, only ATi's GPUs have support for the latest 10.1 revision of Microsoft's all-powerful DirectX multimedia API.
Until ATi releases the upcoming dual-chip version of the HD 4870, we won't know exactly how this latest round of the ATi versus Nvidia battle is going to play out. But after nearly two years of Nvidia dominance, things are already looking much more promising in the ATi camp.