This paper presents an analysis of the performance of the shader processing units in a modern Graphics Processor Unit (GPU) architecture using real graphic applications. The architecture of a modern GPU is described and a simulator and associated framework used to evaluate the architecture is introduced. The paper analyses the effects in performance of different configurations of the shader processing units and compares a classic GPU with a unified shader GPU. The evaluated unified shader architecture proves to be 15% to 30% more efficient, in terms of area, with a 2% to 7% improvement in performance when compared with a similar non-unified architecture.