AMD pits RV775 against GTX285

As indicated by earlier reports, nVidia will release a new GTX 285 and dual-gpu GTX 295 graphics card early next year. These cards are based on a 55nm version of the GT200 and are able to reach higher clockspeeds due to their decreased power consumption. As a response to these new nVidia high-end cards, competitor AMD reveals its secret weapon, the RV775 videochip. 

This RV775 GPU is based on the RV770, the chip used in the Radeon HD4800 series. The chip has undergone several improvements to make it faster, while maintaining the original size. VR-Zone has released detailed information on the new videochip and is convinced that they are accurate. The diagram shows the RV770 PRO and the RV770 XT (HD4850 and HD4870) next to the renewed RV775 PRO and XT. 

  The diagram shows the differences between the RV770 and RV775, source: VR-Zone

The new RV775 videochip will also be produced on 55nm, using the same 256-bit memory bus. According to the diagram, the chip contains 840 shaders, which indicates that AMD has added an extra block of 40 shaders to the modular design of the RV770. The texture units has also been increased from 40 (RV770) to 48 (RV775). This could lead to a maximum performance increase of 20%. 

Apart from the extra processing units in the RV775, the clock frequency has also been raised. The chip is clocked at 900 MHz in the fastest XT edition and 725 MHz in the PRO version. To feed all this extra power with enough data, the graphics memory has also been updated. The GDDR5 memory of the HD4870 will increase from 900 to 1000 MHz. The memory of the RV775 PRO is clocked at 1400 MHz, which makes it probable that the card is equipped with GDDR4 chips. 

Tweaked RV770 has 5% more shaders and 20% more texture units

While the RV775 has more processors, the surface of the chip has shrunken down a little. It's still unknown how AMD managed to do this. It's possible that AMD left out the CrossfireX sideport or another part in the chip. Another option would be that some of the components have been produced even smaller. 

VR-Zone indicates that the new HD4800 card based on the RV775 XT can be expected in January. The slightly slower RV775 PRO will follow two months later. 

Tags: crossfire gddr4 gddr5 hd4870 hd4850 radeon

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