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ATI Radeon HD 4850: Smarter by Design?


Since only the Radeon HD 4850 has been made available for the moment, let’s look at the specifications for that card, along with those of the GeForce 9800 GTX +, which Nvidia has pulled out of its sleeve at the last minute to compete with it (though it won’t be available until July17).

GPUHD 3870 X2HD 48509800 GTX9800 GTX +280 GTX
GPU frequency825 MHz625 MHz675 MHz738 MHz602 MHz
ALU frequency825 MHz625 MHz1688 MHz1836 MHz1296 MHz
Memory frequency900 MHz1000 MHz1100 MHz1100 MHz1107 MHz
Memory bus width2x256 bits256 bits256 bits256 bits512 bits
Memory quantity2 x 512 MB512 MB512 MB512 MB1024 MB
Number of ALUs640800128128240
Number of texture units3240646480
Number of ROPs3216161632
Shading power1.06 TFlops1 TFlops(648) GFlops(705) GFlops933 GFlops
Memory bandwidth115.2 GB/s64 GB/s70.4 GB/s70.4 GB/s141.7 GB/s
Number of transistors1334 million956 million754 million754 million1400 million
Die area2 x 196 mm²260 mm²324 mm²248 mm²576 mm²
Shader Model supported4.

When looking at the main characteristics, first of all the 4850 seems to leave the 9800 GTX, or even its + version, no chance – with 27% more transistors, 800 ALUs, and a theoretical processing power of 1 Tflop, or 42% higher, not to mention support for Direct3D 10.1 and a superiority that’s often quite marked in synthetic tests, as we’ve seen. All that is nothing to sneeze at. Yet, due to its keeping a 256-bit memory bus, memory bandwidth remains a little weak. And AMD still has a clear lag in the number of texture units and ROPs, and seems not to have learned from the errors of the past in that department.

Engraved at 55 nm, the RV770 is a relatively small chip at 260 mm², less than half the size of the GT 200. That’s no longer an advantage for AMD, however, with Nvidia catching up with the 9800 GTX +, which introduced the G92b, a G92 engraved at 55 nm and which, according to our measurements, is 5% smaller than the RV770 thanks to its smaller number of transistors. That, by the way, is the main innovation of this card, and it allows a 9% boost in GPU frequency (and ALU frequency). And… that’s all! All the other characteristics (with the possible exception of temperature and power consumption, which we’ll check later) remain identical. We initially wondered why Nvidia hasn’t called the new card "GeForce 9800 Ultra," and that would appear to be the explanation. It remains to be seen whether this new version really deserves to exist, except that it’s always a positive point for the purchaser to be able to distinguish between the two versions of the GPU (which wouldn’t have been possible with a gradual replacement of the 9800 GTX’ GPU).

Finally, note that the 4850 has the same theoretical power as the 3870 X2, but with an architecture that’s slightly improved, as we’ve seen, and other characteristics that are slightly different (in particular more texture units). So it will be particularly interesting to compare these two cards in the tests.