The PI will develop, refine and test models for the recording process. This includes both phenomenological and fundamental micromagnetic models for the recording head and medium. These three-dimensional models are mainly extensions of previous work. The phenomenological models are intended for the systems designer who wants to optimize performance, and the fundamental models are intended for the materials engineer who wants to understand the relative role of particle interaction on the magnetizing process. Such factors as over-write and track width effects will be analyzed.