This book explores the design and implementation issues of Mission Critical Operating Systems (MCOS) and Mission Critical Computing Systems (MCSS). The topics covered, which range from conceptual ideas to descriptions of concrete systems, have been organized into three parts - Operating system design concept, Real-time operating systems and Ada-based real-time systems. The successful operation of an MCCS depends critically on the way the MCOS performs its function. Therefore the design and implementation of an MCOS is vital. It is clear that the area of MCOSs holds many challenges for researchers in the field. Currently, individual aspects of the problem of MCOS design and implementation are being addressed by various diverse bodies, making the development of an integrated solution difficult. The aim of this book therefore is to motivate researchers to develop comprehensive solutions that can meet the challenges of the future where MCCSs are likely to play an increasingly vital role.