Real-time operating systems (RTOSes) are required to run for years without human intervention, and never fail. Safety is a concern when they control physical equipment. One area of real-time operating system (RTOS) research is looking at the question: can developing an RTOS in a safe language result in a system that an errant process cannot crash? In this paper, we examine the advantages and problems of writing an RTOS in a safe language, namely Java. Then we design, implement and measure the performance of a minimal RTOS to schedule processes as threads on a Sun SPOT micro-controller. © 2012 ACADEMY PUBLISHER.