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Devices for the mobile market have to satisfy a set of challenging constraints. In addition to the classical power, reliability and cost constraints, modern devices often have to be open to third party applications and at the same time provide a closed and secure environment for system functionality. In current systems, this antagonism is solved by maintaining a physical separation of subsystems with contrary constraints. Virtualization technology is a promising solution to safely merge conflicting subsystems on a single processor which leads to huge cost benefits and higher flexibility. Microkernel based hyper visors are an attractive choice for virtualization, due to their reliability and robustness. However, the involvement of real-time constraints remains a challenging factor. In this paper, we investigate how the security and isolation features of the L4/Fiasco microkernel impact real-time applications by comparing thread switching times and interrupt latencies to those of a conventional Real-time Operating System (RTOS). In addition, we demonstrate that microkernel based systems require significantly more cache resources than traditional systems. Finally, we investigate the performance loss caused by cache and TLB interference imposed by an application subsystem which runs in parallel to the real-time subsystem.