This tutorial presents how (commercial) RTOS can be tested on different characteristics going from performance to ease of use. First we define what the characteristics of a good RTOS should be. Then a complete test suite is defined to test these characteristics. Tests are executed on the same platform for different RTOS so that a quantifiable comparison can be made. Timings are obtained via hardware tools in order not to "disturb" the behavior of the RTOS and to have fine grain results for each individual measurement. Finally the technical results are compared with how the users of these products perceive the product quality through a web based market study. In this tutorial, a technical comparison is given between different major commercial RTOS (VXWorks, pSOS, QNX, RTX, INTIME & HYPERKERNEL, NT 4 & CE). The market data is based on more than 5000 answers captured over the last year.