The application of feedback control to computing systems is a promising research area, but has to date been hindered by the almost unanimously perceived complexity in creating control-oriented system models. Computing systems are in fact considered very hard to describe with dynamic models allowing for simple and powerful control design tools, so that complex ones need bringing in to the detriment of efficiency and result assessment. In this work a novel approach to the modelling of computing systems is proposed, in a view to explain and partially avoid such complexity, by capturing only their relevant dynamics with the simplest possible models. The approach is shown to work at least on two relevant case studies, so that a significant gener...