From X-bit Labs: According to industrial sources with knowledge of the matter, the code-named ATI RV790 graphics processing unit is nothing else but the already shipping ATI RV770 chip with higher clock-speeds. The new processor can operate at higher frequencies since its design is slightly refined, certain erratums (which do not affect performance or stability of the RV770) are corrected and process technology adjustments are made.
ATI RV770/790 graphics processing units feature 800 stream processors, 40 texture units, 16 render back ends as well as 256-bit memory bus compatible with GDDR3, GDDR4 and GDDR5 memory types. The RV790 will feature higher clock-speeds, but not increased number of execution units.
Performance increases of the graphics card that is projected to be called ATI Radeon HD 4890 over the existing Radeon HD 4870 1GB should not be high as the difference between two products will be increases of clock-speeds. In case the graphics card designer decides to release ATI Radeon HD 4890 X2, performance gain should be modest as well.
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