The use of microcontrollers in electronic systems is forever increasing. Recently we published a series of articles in Elektor Electronics, describing the 16-bit microcontrollers from the 24F, 24H and 33F families made by Microchip. These modern, powerful microcontrollers have many peripherals and an advanced interrupt structure. Using a Real Time Operating System (RTOS) can help with managing the software structure and timing characteristics of a system based on such a powerful microcontroller.In this article we describe how such an RTOS works.