ent CMU Mach 3.0 microkernel exports simple timestamp and delay abstractions through host get time() and a timeout parameter to mach msg(). While this is sufficient for many purposes, it does not provide the precision or generality required for a variety of realtime applications. In this paper we describe extensions to CMU’s Mach 3.0 which provide users with flexible time-based synchronization and timestamp services. Additionally, we will describe how timing and scheduling services are integrated to allowreal-time applicationsto handle timing faults.