In principle, it should be possible to determine the sustainable memory bandwidth by identifying a simplified machine timing model and inserting the appropriate constants from the manufacturer's literature. In practice, this approach fails on both steps: it is not trivial to identify the appropriate simplified timing model; and vendors do not generally provide the required constants. However, examination of the results of the survey suggests some timing models that correspond to ``reasonable'' values of the hardware constants. It should be noted that these are heuristically derived models, and neglect many details of the actual hardware implementations. They are not accurate enough to be useful for predictions of memory bandwidth, but are more useful for understanding the basic mechanisms involved in determining memory bandwidth, and how the various costs depend on machine architecture.