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ATI Radeon HD 4850: Smarter by Design?
By , Florian Charpentier

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).

Specifications of the main cards
GPU HD 3870 X2 HD 4850 9800 GTX 9800 GTX + 280 GTX
GPU frequency 825 MHz 625 MHz 675 MHz 738 MHz 602 MHz
ALU frequency 825 MHz 625 MHz 1688 MHz 1836 MHz 1296 MHz
Memory frequency 900 MHz 1000 MHz 1100 MHz 1100 MHz 1107 MHz
Memory bus width 2x256 bits 256 bits 256 bits 256 bits 512 bits
Memory quantity 2 x 512 MB 512 MB 512 MB 512 MB 1024 MB
Number of ALUs 640 800 128 128 240
Number of texture units 32 40 64 64 80
Number of ROPs 32 16 16 16 32
Shading power 1.06 TFlops 1 TFlops (648) GFlops (705) GFlops 933 GFlops
Memory bandwidth 115.2 GB/s 64 GB/s 70.4 GB/s 70.4 GB/s 141.7 GB/s
Number of transistors 1334 million 956 million 754 million 754 million 1400 million
Process 0.055µ 0.055µ 0.065µ 0.055µ 0.065µ
Die area 2 x 196 mm² 260 mm² 324 mm² 248 mm² 576 mm²
Generation 2008 2008 2008 2008 2008
Shader Model supported 4.1 4.1 4.0 4.0 4.0

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.

Radeon HD 4850

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).

Radeon HD 4850

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.

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