> Many real world interactions require hard real time and with monolithic kernels you are just not going to be able to meet your guarantees. Lots of hard real

> Many real world interactions require hard real time and with monolithic kernels you are just not going to be able to meet your guarantees. Lots of hard realtime systems (e.g. on microcontrollers) use a RTOS where there is even no distinction between user and system mode, thus one cannot even talk about microkernels vs. monolithic. From a software engineering architectural perspective this is not a good design, but it is very fast (thus the time guarantees you can give are smaller) and sometimes easier to guarantee runtime guarantees. And it is easier to write a RTOS where all things run in system mode (which does not imply it is easier to debug bugs or to maintain).