A method for evaluating the differences between computer systems is provided. The systems are evaluated using one or more differential rule definitions and one or more differential rule sets. The rules evaluate the differences between specific parameters in the computer systems and are used to generate a score that indicates how different the systems are based on these parameters and preferably what the cost to remedy the difference would be. The rules can be used for consolidation analysis, compliance analysis etc. The rules each include a weight that quantifies the importance of the rule to compatibility and the score is affected accordingly. Systems can be evaluated against each other or against themselves at different instances in time.