except it really isn't an operating system - i used it back in the 1980s, and it is really just a static library you can call into - same as msdos. there is no OS process running things.
Many RTOS don't have processes, only tasks, which depending on the nature of the OSes can be cooperatively or preemptively scheduled. Also everything is linked together and deployed as a single execution unit into the hardware firmware.
So again, by the same definition, when using cooperative scheduling, they aren't OSes.
just what i said about cp/m