DioneOS (pronounced /djoneos/) is multitasking preemptive, real-time operating system. The system is designed for Texas Instruments MSP430x microcontrollers. Target microcontroller platform has limited resources,i.e. system clock frequency in tens of MHz and memories amount from tens to a few hundreds KB. The system is adapted to such conditions by providing its compact and efficient image.The efficiency term means here minimization of additional CPU load caused by the system usage. According to this definition, the system is more effective when it consumes less CPU time for execution of its internal parts (e.g. threads management).