In this paper, we explore the problem of designing an effective master-slave operating system architecture for multiprocessors and describe current status of our prototype implementation, called APRIX (Asymmetric Parallel Real-tIme KernelS). This work has been largely motivated by the recent emergence of heterogeneous multiprocessors and the fact that the masterslave approach can be easily applied to heterogeneous multiprocessors while SMP (symmetric multiprocessing) approaches are restricted to homogeneous multiprocessors with UMA (Uniform Memory Access). The purpose of this paper is to identify and discuss design issues that have significant impact on the functionality and performance of the master-slave approach. Specifically, our study will investigate three major issues: structural design of a master-slave operating system based on our experience with a prototype development of APRIX, functional design of remote invocation mechanism that is required for executing kernel mode operations on a remote procesor, and performance improvement via application-specific kernel configuration. We finally describe our initial implementation of APRIX and preliminary experiment results.