AMD unveils fastest ATI GPU yet

The ATI Radeon HD 4870 X2 graphics board houses two 4870 graphics processing units (GPUs) and competes with Nvidia's fastest board, based on the GTX 280. In chip-to-chip competition, Nvidia's GTX 280 generally beats a single 4870 in performance because it's bigger and faster: the Nvidia chip packs 1.4 billion transistors onto one chip, while ATI has about 950 million.

But because AMD puts two chips on one board and has improved chip-to-chip communication, the 4870 X2 is expected to equal or exceed the Nvidia chip in many cases.

AMD has introduced a more advanced cross-GPU connection technology based on the PCIe Generation 2 standard. And the 4807 X2 can use two gigabytes of memory, compared to most high-end boards that use a maximum of one gigabyte. It also uses memory based on the new GDDR5 standard.

One of the central challenges for AMD is to make sure the performance scales up efficiently when more chips are added. This is the crux of AMD's strategy: Instead of building a large monolithic--albeit fast--chip as Nvidia typically does, AMD takes smaller chips and gangs them together for better performance.

To date, the results for multi-GPU performance have been problematic, typically another board will deliver only 1.5 times better performance. AMD is targeting 1.8 the performance with two chips running games in high resolution, and with four of them, about 2.5, according to earlier comments from Jon Peddie of Jon Peddie Research.

Game PC vendors expect good things. "(The 4870 X2 is) more than a match for a single Nvidia GTX 280, and depending on the title sometimes a match for two GTX 280s," said Kelt Reeves, CEO of game PC maker Falcon Northwest. "Drivers are now ATI's only weak area, so the 4870 X2's performance and scaling with two 4870 X2s (QuadFire) often varies widely from title to title," he said.

In September, AMD is also expected to bring out the HD 4850 X2, a dual-chip board with slightly lower performance. The higher-end 4870 X2 is rated at 2.4 TFLOPs (or teraflops, a common yardstick for raw graphics chip computing power) and communicates with memory at 230GB per second, while the 4850 X2 is rated at 2.0 TFLOPs and has a memory bandwidth of 128GB/sec. Both boards will integrate 1600 stream processors, which do parallel processing on streams of data.

The 4870 X2 is priced at $549. Nvidia preemptively responded to this by cutting the price on the GTX 280 to $499 in July. The lower-end 4850 X2 will be available in September for $399.