The Automated Material Handling System (AMHS) must be designed effectively so that it never becomes a limiting factor for the capacity of 300mm wafer fabs. Ideally, a fully integrated fab simulation model (i.e. a model containing detailed modeling constructs for the production operations, the tools, the AMHS, and tool AMHS interactions) should be used in order to design the AMHS. However, the problem is that it takes too much time to simulate and analyze these models. Experimentation has demonstrated that certain capacity models with less detailed AMHS representations can generate accurate system predictions in comparison to the values produced by fully integrated models. Because these less detailed models run faster, we can thus assess efficiently the effects of an AMHS design configuration on equipment capacity. A case study comparing the computational efficiency and the quality of the performance predictions at different levels of detail will be presented.