Notebook users had to wait six months for AMD to fashion Mobility parts out of its Radeon HD 4000-series desktop graphics processors. The company apparently decided not to impose a similar wait for that architecture's die shrink, because it's just announced a pair of mobile GPUs based on a brand-spanking-new 40nm GPU.
The Mobility Radeon HD 4860 and 4830 are purportedly the world's first notebook graphics processors based on 40nm process technology, but they're not high-end parts—or straight die shrinks of the RV770, for that matter. AMD has outfitted the GPUs with 640 stream processors (down from 800 on the RV770) and 128-bit memory interfaces (down from 256-bit) with support for both GDDR5 and GDDR3 memory.
Before you turn up your nose at the memory bus width, consider the following: with the maximum supported GDDR5 memory speed of 4GT/s, the new Mobility Radeon HD 4860 should have up to 64GB/s of memory bandwidth at its disposal. By contrast, the desktop Radeon HD 4850 only has up to 57.6GB/s despite its 256-bit interface, because it normally uses only GDDR3.
The narrower memory interface, reduced stream processor count, and smaller process also resulted in a smaller, less power-hungry chip, which has allowed AMD to ramp up clock speeds. These 40nm mobile Radeons can run at up to 650MHz, a whole 100MHz faster than the top-of-the-line Mobility Radeon HD 4870. AMD quotes 832 gigaFLOPS of peak floating-point power, too, which isn't that far off the Mobility Radeon HD 4870's 880 gigaFLOPS. (The 4870 does, however, have significantly more memory bandwidth—up to 102GB/s). Put all that together, and AMD claims the Mobility Radeon HD 4860 outperforms the RV770-based 4850 by a small margin in 3DMark06.
Unfortunately, AMD stayed mum on its release schedule when it briefed us about the new GPUs. The company nevertheless mentioned that it was "working with quite a few OEMs to launch this product," and it said we could "presume that this [launch] will be tied to one of our partners." You can probably look forward to Mobility Radeon HD 4860- and 4830-powered notebooks in the near future.
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