Abstract. In this article we elaborate on portability in componentbased operating systems, focusing in the hardware mediator construct proposed by Frhlich in the Application-Oriented System Design method. Differently from hardware abstraction layers and virtual machines, hardware mediators have the ability to establish an interface contract between the hardware and the operating system components and yet incur in very little overhead. The use of hardware mediators in the Epos system corroborates the portability claims associated to the techniques explained in this article, for it enabled Epos to be easily ported across very distinct architectures, such as the H8 and the IA-32, without any modification in its software components.