My semester thesis (Studienarbeit) is about operating system mechanisms to save energy for hard discs by using cooperative strategies. You may download the thesis in PDF format. It's written in English. The thesis has evolved into a paper that has been published in the Proceedings of the Fifth Symposium on Operating Systems Design and Implementation (OSDI '02). You may download the implementation, which is a patch to the SuSE Linux 2.4.10 kernel sources.