Processor architects have a challenging task of evaluating a large design space consisting of several interacting parameters and optimizations. In order to assist architects in making crucial design decisions, we build linear regression models that relate processor performance to micro-architectural parameters, using simulation based experiments. We obtain good approximate models using an iterative process in which Akaike’s information criteria is used to extract a good linear model from a small set of simulations,and limited further simulation is guided by the model using D-optimal experimental designs. The iterative processis repeated until desired error bounds are achieved. We used this procedure to establish the relationship of the CPI performance response to 26 key micro-architectural parameters using a detailed cycle-by-cycle super scalar processor simulator. The resulting models provide a significance ordering on all micro-architectural parameters and their interactions, and explain the performance variations of micro-architectural techniques.